studying for college entrance

i have a very important college entrance exam in three months and i am two years behind all my previous classmates because i had to take two drop years because of my mental health (i also have bpd)
i can’t focus or “lock in” like other people i do the needful, study for shorter periods of time rather than studying not at all but most of my energy is wasted by how much i think. i want to get up i want to study ill think about the consequences and what will
happen if i don’t score and if i don’t get to go to college again this year. i can’t stop the overthinking and most of my energy goes into this and hence when i do get up to study im just so exhausted