Don’t be found ~てはだめだ


Grammar Explanation

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While telling ghost stories at night, Rize relays the tale from her childhood, of a frightened servant walking home one night. Rize says the culprit was her, practicing sneaking around and crawling through the bushes.

バラしちゃだめじゃん!!」
Don’t be found!!”

Note that じゃん is a short form of じゃない, the negative of だ.