I had to make this decision last year aswell as my lowest grades were in bio and psychology. I was doing way worse in biology compared to my other subjects but didn't want to drop it because my other subjects were 'less respected'. However ultimately I would have not got accepted into uni with bio at A2 because my predicted grade would have been too low. Also the course I wanted to do didn't need a science so I dropped it. Psychology is much easier, at the end of the day I just want 3 good grades, I'm not too bothered about the subject they're in.