A level choices??

Is it a good idea to do Maths, chemistry, and biology with psychology as a 4th AS level? I know doing 3 is enough but my school requires me to do 4 AS levels so I'm unsure if psychology would be a good 4th because I've heard it's really content-heavy?
I'm also considering business, economics, or geo as a 4th but I have no idea what will go best with my 3 main ones.

I do bio, chem, maths and geo. I will say geography goes very well with subjects like economics or business but I think it has a lot of skills that can be transferred into those 3 other subjects. Psychology, I’ve heard, has a lot of biology in it which I guess biology could help with.

All those choices sound pretty good! Psychology is nice because, although it's content-heavy, it has extended writing, which shows universities that you're not just a memorising machine (which can be particularly true for biology). You'll be able to write well. I don't know what geography's like, but if it has extended writing questions as well that'll be another good choice. Psychology and geography are both science-related subjects, so they should synergise well with the other three. Economics/business I don't know so much about, but as you already have three facilitating subjects, it should go pretty well, especially alongside maths, and give you some variety in your first year.

Do you have any plans for what to study at uni, or what you want to do later on? That'll help you work out what choice will be the best. With your main three a-levels, though, you'll have a LOT of options when it comes to science. Don't stress out too much about your fourth!