The first two are perfect. The third is perfect, but the parentheses should be (at work). If it's happening now (progressive), make it "are screwing up," and if you're talking about the work day that is over, "we all screwed up." Depends on your meaning. The fourth: this is an old, even antiquated use of the word "screwed" that you will probably only see in literature. "Screwing up" eyes doesn't really help anyone, so it isn't really correct. Remove "to help" and it's correct, but remember that this is an old usage and you probably won't see it anywhere. Don't say it, it will confuse people. Can just replace with "She looked up." The fifth: "Mary screwed up her friend's full name." The sixth: "screwed up" is used right, but the sentence doesn't look right. I would change to," What happens when you screw up is that you get discouraged," or "You get discouraged when you screw up." But don't get discouraged! You're doing great. The seventh: Pretty good, I would simply change "admits" to "admitted" and "so" to "and."

Yes, you should listen to Angela. It's good to have a teacher who is comfortable telling people they are wrong, and who has the confidence to instruct people what to do.

sorry, but you can write here if you want, you version, under my comment thank you for the advice!

John made a lot of errors. (and missed a lot of errors in your sentences.) You should have waited for more responses before choosing "best answer." In the future, get more than one response.