I had to fight like mad to do 4 A-levels, I ended up doing one on my own (did AS with an adult learning class thing, one night a week, incredible waste of time so did A2 on my own) I think if you reckon can handle it, and are doing it for enjoyment more than anything else then go for it. The way I saw it, if I didn't do the A-level I'd be doing it anyway but without the certificate at the end.
If your teachers dig their heels in, find somewhere else that offers french, to learn it like that could be really cool!! The experience of working solely on your own could also be really valuable!