I would't sweat it. Lecturers have different views anyway. During my Masters course I had one who went through each essay crossing commas out (a younger one) and another (an older one) who went through them adding commas in! Never caused a loss of marks.
It depends when your lecturers were taught grammar. I was taught comma use in the mid-70s and the rules have changed since then. From what I've seen, commas seem to be out of fashion at the moment. Some recent peer-reviewed journal articles I've tripped across, have been almost unreadable thanks to a lack of punctuation.
Incorrect comma use is unlikely to be a source of serious - if any - percentage loss. Even if marks are docked, they will be minimal. Your first year results generally don't form part of your final degree grade, giving you a year to get the hang of how things work at your particular uni.