As above, I know it's really really difficult but try to forget about it on results day. Stressing won't change it now, and remember that grade boundaries usually tend to be relatively low for chemistry anyway - you don't need 100% so it's fine if you didn't know some stuff. If you get a 6, you could also resit in year 12 as a lot of people do resit their GCSEs to match for vet schools, and you could also look at some unis which will accept a 6 - the requirements vary a lot in each vet school and also there are things like gateway and prelim 6 year courses. Even if worst happens, this isn't the end of the road, you have options to consider. Unfortunately I can say that exam stress never goes away even at vet school (I never actually experienced it until I started) and so finding ways to manage it early on is good - focus on any other exams you are sitting and then distract yourself with doing things you like until results day, as much as it's easier said than done.