When you say that you did fine at AS, did you meet your targets by a sizeable margin, or where they closer? If you struggled a little with the workload, or are in danger of not finishing with a good grade in one of them at A2, then dropping one may indeed be a possibility. Which is your strongest preference out of biochemistry, chemistry and modern languages?
I did do at least 4, and I thought the workload was challenging at times, but manageable. In hindsight, I only really needed to take three to meet my offers, and a lot of that time spent taking on as much work as I did could have perhaps been spent doing other things. I did an EPQ, which was also unnecessary, but I at least found it more stimulating than some of my A-level modules, and I don't regret doing it -- it wasn't as much work as a regular A-level, and I had a lot of fun pursuing something which I had a genuine, passionate interest in at that stage. (My grades are in my profile.)