Preceptor taught me wrong and I got chewed out

First of all the IV cannulas that don’t self stop are my natural enemy. I always end up making a mess with them. Second of all, my first preceptor I had taught me how to draw labs with the vacutainer directly into the tubes, not into the syringe first. When I rotated to a new preceptor she saw me do it and chewed me out for contamination and not following policy. I cried right then and there, and I’m not even a cry baby. I was enjoying all my time in the ED so far and now I just want to quit, because what kind of culture is that? I’m not going to quit. But I wish I had a do-over, because how do I even defend myself after that?