Failed Nat 5 math want to do dentistryWatch
However, what you need to do depends on you, and how you feel. You seem to have a very clear idea of want you want to do, which makes it easier to set yourself goals to achieve that. So set those goals for yourself clearly now, focus on the subjects you need for what you want to do, for dentistry. Make it easier to accomplish those goals.
Do you feel like you are putting too much pressure on yourself this year? You're taking six subjects, which is quite a few. Some people, as you may know, prefer to take the subjects they need earlier, have the security of attaining the required grades early, and then add subjects they enjoy later, to bulk up their personal statements, say, or just because they enjoy them. That may be something to consider, given that you seem to be worried about your maths.
Or maybe you do really enjoy them all and want to take them, and want to make as competitive an application as possible, in which case, being ambitious isn't a bad thing, as long as you can keep pace with your ambition. I would one hundred percent encourage you to follow your academic interests, of course whilst being realistic.
But that's on you. I don't know you. I've just been through the same system not that long before you. You need to know yourself. Be realistic, or maybe just a little bit more optimistic than realistic. Don't push something onto yourself just for the sake of it, and don't give something up because you feel forced to. Make sure you're having conversations with your teachers, asking for help or advice from them if you need to, and obviously remember that the last couple of years have not been easy on everyone learning-wise.
Don't stress about not being accepted by unis. Just by showing willingness to do higher, you're showing how committed you are, keep doing that. It wouldn't be a bad idea to do higher, as it would definitely show capability and the skills they are looking for. But you will not get rejected just because you don't have higher, as long as the rest of your application is good, too, so don't just focus on maths!
Hope that helps