I believe we're in similar situation. I am in engineering but just moved into the labs recently. I was doing some design calculations, i went to my industrial supervisor to get it checked and he kept on sending me back to get it corrected. No matter how hard i tried to get it right, he always found a valid reaon why the solution was wrong. I went back to the drawing board and after hitting so many walls, not to mention the headache involved, i believe i may have got it right this time and using my own method which made me really pleased with myself.
If you take the advice you're given and learn from you mistakes + patience, i think you'll do okay. I am only in my 3rd month by the way