need advice

i’m currently working in retaking 2/3 a levels my third one i got an E in but i didn’t decide to do it as i felt like biology was super hard for me and thinking about doing biology brings up hard memories. However recently my mental health has been better and i’m thinking of also re doing a level biology again. I’m thinking of this because i’m worried only improving 2 of my a level grades won’t get me into a good uni i want but at the same time im also worried that i’ll fail again and not do good. i just feel kinda stuck :(