Yes, I typed "too quickly" instead of "too fast" and was marked wrong, too. I hope the DuoLingo team are reading our comments and can improve the course so that it accepts alternate translations as well.
While quickly is grammatically correct in English, do people refer to speeding drivers as too quick?
Nope, it's just that the stock translation of 빨리 is "quick". However "drives fast" is more idiomatic english
I put that and they marked it wrong, but I think it's more correct than the answer they give.
너무 messes up a lot of people this way, but more often than not it means "too" as in like too much of something