Every time you paint or draw you get better, so keep working.
Was it your effort in the class that was lackluster, or was it your results? There is a difference. Always strive to do your best and you will get better.
It's OK to not be satisfied with your work. It means you're improving. It means you're starting to see weaknesses in your work on your own, instead of needing people to point them out. That means you understand the concepts and know how things should look, which will allow you to improve your skills.
BTW, the still lives are good, especially the cans.