I feel the same. I am a year 13 student waiting on results for medicine, I felt the same when I was in your situation and I feel the same now. The UCAT was a terrible experience for me, and I didn't even do it the first year. I completed one A-Level last year in psychology and I am waiting on two results now but I have an offer. I couldn't take my sciences last year as I had to stay home, my sister was very very unwell and I felt very lost.
It will get better. Your UCAT is difficult but if you struggled (like me) make sure that you get a high band in your SJT and then look for universities that don't place huge emphasis on the average score. My personal statement was very daunting, I had no idea where to start. Im sure there will be one for dentistry, but I found a student room thread that had lots of personal statements for medicine and what kind of offers they received. I'm sure there will be one for dentistry. From there I highlighted common themes to talk about, and took some non-common but great ideas and started from there and made it personal. Take your application one step at a time. Volunteering and works experience can be hard to find, if you have a job im sure you will be able to twist it to point out some relevant experience there.
You still have lots of time, please don't worry. If you start now you will be successful, take a few days to clear your mind and get a start. Look up tutorials for A-Level sciences on YouTube and how people have succeeded in them. My journey into getting my offers was really terrible and im feeling in limbo like you (because of A-Level results), but if I got through it you can too.