Really not sure what to do...

Okay so I'm really certain on what university I want to go to but the grades are quite high, and I'm worried I won't get them... If I put an insurance choice and get rejected from my first choice do I have to go to the insurance uni? Can I apply for the same course as my first choice through clearing? How does clearing work?... Sorry for all the questions, but I'm kinda uncertain about all of these things.

If you miss your firm offer and your firm decides to reject you (missing your offer isn’t an automatic rejection - they can and often do decide to accept students with lower grades if the university has space and believes that the applicant has a chance of succeeding on the course) then you are placed with your insurance (assuming you meet your insurance offer or they decide to accept you with grades below your insurance offer).

It’s possible to ask your insurance to place you into clearing but this takes some time (24-48 hours in most cases). Applying back to your firm for the same course they rejected you for is not likely to be successful - they will already have considered whether they can take you with lower grades before rejecting.

You can apply to any course with vacancies in clearing. But just because there’s vacancies doesn’t mean that any grades would be accepted.