Would "Oh, wrong museum" also be acceptable?
I hate duolingo: Small details who makes no difference is considered wrong. How annoying. "oh, wrong museum" should be correct.
When you see something like that, report it and it gets fixed soon
Here "Oh" is allowed, but in other questions you are forced to choose "Oh wow" instead. This is inconsistent.
That might be because "oho" can mean different things depending on the sentence. In this one, "oops" might work, too.
Can i use "väärin" instead of "väärä" in this case?
No, väärin is an adverb. Here an adjective väärä is required.