a level resits

hi,
im just about to finish my a levels, and i feel like i haven't done well enough to get the grades i need for uni. i have had two separate exam clash days, meaning 4/9 of my a levels were overlapping. this has been very overwhelming and i feel like it has lead to me underperforming from exhaustion.
does anyone have information about exam resits. i know very little about them and there's not a lot of information online. i am very anxious and need to plan far ahead for every outcome, and this feels like a very possible one.

how many a levels did you do>?