Surgery room or, more often, operating room, is used in American English. British English's "theatre" is very strange in this context to Americans. That said, the course generally accepts British and American English translations, so I'd suggest reporting it.
Yes it does sound dumb, but American English and British English (and indeed all languages) have dumb sounding phrases if taken literally. The only point here is, "operating theatre" is indeed its name in the UK, and should be accepted.