A Surprise (Titles should be capitalized) 

Have you ever received a really wonderful surprise? (had = posessesion, you do not own surprises, you receive them) Well, I have. It was a present for my 16th birthday. My parents decided to make me genuinely happy and bought me a ticket to the International Space Station.
The next day my dad told me nothing and just directed me to his car. ('to go to' sounds weird. We know where you're going, to the car.) Two hours later, I saw a magnificent space shuttle. Then my dad gave me a ticket and said had a nice journey. ('just' sounds unnatural and unnecessary.) I always dreamed about dissecting the universe, but I knew that my parents were on a tight budget and couldn't spend a fortune on my present.
When I reached the station, I was very curious about everything there. The people in the station seemed hardworking and dedicated to their careers, so I thought that it would be better to take a tour through a station by myself. Of course, I had a nose for trouble, so I couldn‘t not to open the doors with the note ''DO NOT ENTER''. (who couldn't not open the doors? I couldn't not open the doors with the note...) I saw a lab where new forms of life were investigated. ('the' sounds awkward.)
Two days later I was back; the hustle and bustle of the journalists importuned me till the late evening. I felt like a superstar but finally I said, ''I won‘t tell you anything, not even my parents, because something I saw where can change our life strongly''.

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Semicolons (;) connect two sentences, indicating a longer pause than ',' 
Before a person speaks when it's in the middle of a sentence, there should be a ',' before the quotation marks (" ")

My sister smiled and said, "how are you today?"
He stopped running with a loud sigh and faced me, "I'm ready to go now."