Well because your in College, I may be saying the wrong things here, but I'll give it a shot anyway.
How does the rest of the class feel about that paper they got wrong? Maybe ask them about what they did wrong and if they have the same situation and maybe you could come
When I was in Highschool, writing was my strongest assest, still is to this day, I just don't go to College though.
Do you know any of your old Highschool teachers that taught you Language arts? I would maybe get in touch with them and ask for advice, I did that once with my old L.A teacher and it made a difference.
Maybe I can even help you, maybe show me a paragraph and give me an example of what you have to do. I did a few papers for my ex-girlfriend in her first year of college and she got a 90% on one and a 95% on the other.
Also, if you get that nagging suspicion, just think it over for a lil while and make your best judgement and don't overthink whether or not it's what the author was going for. Not every writer can detect anothers metaphors down to a tee you know, if we all could, all our papers would look the same.
Also, this might sound dumb to you because theres money involved with your education, but don't get frusterated, that never helps, try and take your time and focus.
I hope I was of some help.