hey, i understand that it may not be nice to see those grades but i've heard many schools do mock exams at the start of year 13 to see if anybody has improved and change any predicted grades if necessary. the best thing i can tell you to do is just use these grades as motivation to try even harder to reach the grades you want and need in any more tests you have, whether that be trying out new revision styles or just going over content/exam technique again. predicted grades are also based off topic tests as well as mocks (at least they are in my school) so your topic test grades will definitely be accounted for.
away from grades, if you still take the ucat and do well in that then assuming you have a really good personal statement with relevant work experience, then you definitely still have a chance. doing a little bit everyday honestly can make a huge difference and you still have time to change things, even just making weekly goals to go over one topic in a subject can help you a lot. nothing is going to change if you dwell on it for too long. the quicker you take action on it, the quicker you will be able to see improvements. you can get through this and still become a dentist!