"Romance movie" is absolutely correct and more common than "romantic movie". ROMANTIC is an adjective. "A romantic movie/book" "A romantic night" "A romantic poem/story" ROMANCE is a noun. "It was a short-lived romance" It can also be an adjective when used to describe a type of writing: romance novels.

I would disagree with Marcin about 'romance movie' being more common than 'romantic movie'. Certainly you can say that the story is 'a romance', the same way as you'd describe a story as 'a thriller', but I would always use the adjective form before 'movie' or film: 'a romantic movie' or 'a romantic film'. Out of curiosity, I googled this and found one or two references to 'romance movie' and dozens to 'romantic movie'. This could be a regional difference, but I have never actually heard anyone say 'romance movie'.