لا ادخل في الغرفة
Yes, it is.
"laa 2adkhulu" -- formal standard.
So: I do not go into the room is wrong. Well, well, silly me!!
Hahaha. But at least you can know in your heart that right is on your side, and be generously indulgent towards Duolingo and its imperfections. They're only human, and it must be difficult to think of all the possible translations.
The English sentence is very strange. The present simple (I enter/I do not enter) is almost always used for habitual actions, so this would really mean "I never enter the room".
Well, it's possible to imagine situations, like replying to, "What do you do when you pass that door?" It may be a little strange, but it's not impossible, and it's certainly grammatical.
Didn't is the contraction of did not, which means the exact same thing.... update acceptable answers immediately