I'm only in my first year but I've encountered a good bit of gen chem, biochem, and o-chem in my physiology, immunology, and pharmacology courses. I wouldn't say I feel confident in my biochem/o-chem knowledge either, but I'm doing well. The material we use from those courses is typically general/broader concepts that you probably know more about than you realize. Or it's something you can quickly review with a youtube video. I wish I didn't listen to the people who told me you don't use certain prereqs for vet school. I loved biochem and my background knowledge helps me grasp certain topics faster in physiology, whereas in pharm I had to go back and review some chemistry. You'll be fine either way. I wouldn't recommend studying before vet school, just review the topics you need to know as they come up in lectures. It's rare that I have to go back and review things from prereqs, but I do it occassionally