If I understand your dilemma, you can take the exam on wednesday, and if the grade is your lowest, the instructor drops that one. If you don't take the exam, then this is the exam grade the instructor drops. Presently, you are passing the course.
It sounds like you have nothing to lose by taking the exam on Wednesday. This is just Monday. Sometimes we find that when we "totally don't get it," it's just a small detail we aren't "getting."
My advice, since you asked, is to get with somebody who knows what they are doing (the instructor, maybe, or somebody in the math lab at school), and see if they will spend a little time with you on the very basics
, since it sounds like that's where you got off track. It could be that that one little tiny detail will result in an "aha!" that puts trig at the top of your fun things to do list. (Happened exactly that way for me with physics--not passing, even my instructor used to borrow my calculator during exams because, as he said, it appeared I wasn't going to need to use it!!! Came out of my nosedive after 2 failed exams, got an A- the first semester and a perfect
score on each exam the second semester. My classmates hated me!!!!
How did you do in geometry? Trig is nothing more than using names for relationships you played with in geometry!
So, I'd say, in any case, stay calm and take the test on Wednesday. You are already passing, you have nothing to lose and everything to gain!
Good luck and let us know how it works out.