I was in the exact same situation as you last year, I’d applied for Maths, Biology and Geography, but was having doubts about Geography. I switched for Chemistry and I’m so glad I did. Chemistry compliments Biology really well and makes a lot of aspects of Biology easier to understand. It opens more doors too. It’s your decision at the end of the day, but as someone who’s been in the same situation as you, I really recommend switching Geography for Chemistry.