В + accusative indicates direction (into, towards) and в + prepositional indicates location (in, inside). Here комнату is the accusative case, so it's "to the room." If it the door was inside the room it would be в комнате.

to the room :в комнату in the room :в комнатe

A context-search at reverso.net returned a number of instances where that phrase is used to mean a variety of things, including "the door to the room", see:
http://context.reverso.net/translation/russian-english/%D0%B4%D0%B2%D0%B5%D1%80%D1%8C+%D0%BA%D0%BE%D0%BC%D0%BD%D0%B0%D1%82%D1%8B

Is there some particular reason you're asking a question is what may or may not be good Russian, in a course for English-speakers?

When use only Russian, you're denying yourself possible input from someone who can answer your question, but doesn't yet know enough Russian to understand fully what you're asking.

I usually ignore such questions, and certainly never try to answer them, even though I'm starting to accumulate a lot of information which has proven useful to others here. So, try English next time - you might actually get an answer to your question.

Your choice is fine. Report it when you will come across on this task next time.