I have heard that every so often from one student or another. Let me tell you that is inefficient.
First, your brain has indeed managed to retain something from what we have gone throught since last course, nearly in spite of you. I am currently trying to learn italian, at my own pace and with looong breaks without touching my textbook. I am amazed about how much I retain everytime, without doing anything.
Second, will you study more if we cancel the course? Not likely. The only way to keep up with the little motivation you have, is at least to take advantage of regular courses.
Third, words and grammar situations have a way to reappearing. If you haven’t learnt a word, it isn’t as if you had missed a course about a theorem, which your math teacher will never go back to. If you don’t know a word, you’ll hear it eventually again, probably soon, and if you don’t, well, it doesn’t matter: you obviously didn’t need it.
So, learn three words correctly, no matter which ones, and come to the course. You’ll shine.