What can I do as to not retake calculus 3?

It seems like you have test anxiety. So I would suggest you practice taking a test. Instead of just doing the problems in the book, select 5 or 6 problems and do them with a timer and no notes. Also, see if you can get any previous exams from the class. You seem to know the material, but freeze when it comes to tests so you should work on that specific problem.