I think you made a very good decision there.
I was the same as you in yr 10. i had two electives (french and german). And i thought (stupidly) i can't do both, that would be crazy, it would be too hard. I thought (stupidly) that I should do an essay/humanities subject like history, to add balance to my subject selection.
Long and short, i dropped german and did history instead. I disliked history, and found it much more work than german had ever been, and besides, I'd enjoyed German more (when you enjoy it, it's way easier to motivate yourself).
Languages aren't really extremely hard in yr 12. They're not knowledge-based (i know that sounds counterintuitive with all the vocab, but it's true). like that person above said, they're more like a skill. (Modern) languages are so much more relaxing than other subjects where you have to learn a ton of content.
The only thing i would suggest is that make sure you put in a good amount of study in your own time. (eg. watching the news, reading books, listening to internet radio in the language, doing practice tasks etc). It's pretty fun compared to studying for certain other subjects (english...)
Anyhow, if you're good enough, and you like it, go with it. I know several people who do two languages (and i don't go to a selective school). Just don't let one language take over (if you learn a word in french, make sure you know what it is in german and vice versa... otherwise one language will evilly supplant the other.)