I'll do as many as I have time to do now.  If I find more time later, I'll correct some more.

Corrections in red.  Stylistics in blue.  If I omitted a sentence, it's because it's correct.

- When babies are in the mother's womb, they stay remain in a curled position. Then, when they are born, they begin to crawl.   [This sentence means that babyies begin to crawl as soon as they are born.  I don't think babies do that.]

- Maintain your poise. We will make it through.
- Don't creep away as soon as you finish your lunch! You never lift a finger to help, but take advantage of our kindness!
- I don't mean to undertake this way. It's too crooked!  I do not understand these two sentences.
- Please stop humming. I've got a hangover. 
- Entertain [good alternative: Distract] the teacher while I peek at the test results.
- He is so struck by her that he can't see her greed.
- Fancy that.  He begins to stammer every time she blinks her eyes. He is totally struck by her!
- You're so sloppy that you don't appreciate the worth of things.   
- He rages everytime somebody wakes him up from his nap, and slams every door he comes across.

I have to stop here for now.  

I was just wondering if these sentences are correct..

- Stop delaying hesitating! Call him already! delaying requires an object...delaying the game, for example.
- Look beyond the horizon.
- When babies are in the mother's womb, they stay curled up. Then, when they are born, they begin to crawl stretch.  They don't crawl until they are about 8 or 9 months old.
- Poise Compose yourself. We will make it through.
- Don't creep away as soon as you finish your lunch! You never lift a finger to help but you take advantage from our goodness!
- I don't mean to undertake this way. It's too crooked! Not correct
- I don't want to undertake this career. correct
- Please stop humming. I got have a hangover. correct
- Entertain the teacher while I peek the test's results. correct
- He is so struck on her that he can't see her greed. correct
- Fancy that! He begins to stammer everytime she blinks her eyes. He is totally struck with her! not correct.  Stuck ON her.
- You're so sloppy that you don't appreciate things' worth. Your parents shouldn't have spoiled you so much. not correct
- He rages everytime somebody wakes him up from his nap and slams every door he comes across. correct
- A witness asserted that she didn't ignite the fire.
- You can't exploit the class' geek to have your homework done! correct
- It's high time to stop eating fattening food. Summer is coming soon! correct
- Stop scratching your belly. It's getting all red. correct
- It's high time I had my hair trimmed.
- She wears a different disguise according to depending on the person standing in front of her. correct
- Salt fades out as you drop it in a glass of water. incorrect
- Let's go straight, I want to take a walk along the seaside. correct
- She turned down going the trail with me.
- Where are all the blankets I had huddled? They faded away! incorrect
- Let's play hide-and-seek inside my burrow. strange, but correct
- Please don't forsake me. You can't torn apaer all that we've been making throughout these years. incorrect
- My kids used to doze off everyday when they were little. correct
- Please don't toss the dust into the toilet. correct, it's difficult to toss dust, but it is possible.
- I couldn't eat sushi because I don't like raw food. correct
- He struck me with a basketball.
- It's two weeks overdue by now. correct
- I hate bright lights. I prefer dull ones. correct, dim is more common to describe lights
- Have you checked the tuna's deadline expiration date? incorrect, unless the tuna is working on a project that must be finished by a certain time in the future.
- She has never disagreed. She has always nodded. incorrect-a nod could indicate agreement or disagreement.
- The chocolates they made have a perfect shape. correct
- This rock is so rough that it could pierce my face. correct
- He cooped us up in the house to make us clean it. correct
- Stop hassling me with your matters!  correct, but strange

t to do and are so nice to correct them xD
:3
Like

- A witness asserted that she didn't ignite the fire. [better in this context:  she didn't start the fire.]

- You can't exploit the class geek to get your homework done!
- She wears a different disguise according to the person standing in front of her.  This sentence is grammatically correct, but it's hard to understand.   
- Salt disappears when you drop it in a glass of water.  [Alternative: Salt dissolves when.....]
- She turned down to go the trail with me.  Sorry, I can't understand this sentence.
- Where are all the blankets I had put in a pile? They've disappeared!   "huddled" was hard to understand in this context, so I assumed you meant put in a pile.
- Let's play hide-and-seek inside my burrow. ??  "burrow" is not correct, and I can't understand what you want to say.
- Please don't forsake me. You can't tear apart all that we've been doing throughout these years.
- I couldn't eat sushi, because I don't like raw food. 
- He struck me with a basketball.
- I hate bright lights. I prefer dim ones. 
- Have you checked the tuna's expiration date?
- He cooped us up at home to make us clean it. 
- Stop hassling me with your business!
- Cancel all of your tasks. I need your help today!

They're so many, I know. Hope you don't have much to do and are nice enough to correct them.

Regarding the ones I didn't understand, if you paraphrase in English, or write it in Russian, I'll try again to help.