Meaning of てなきゃ in this sentence?

Question

While playing a Japanese mobile horror game, a girl appears with a knife in hand and says the following:

「おとなしくしてなきゃダメじゃない」

I can guess this probably means something like It's a problem if you don't stay quiet, isn't it? but I have problem parsing the てなきゃ: is it from してある (state), as in ドアをあけてあった?

Is the "transitive verb"てある grammar at work here?

Answer 1

してなきゃ is していなければ, and it's the result of these three contractions:

1. していなければ → してなければ (-inai to -nai / -iru to -ru / -imasu to -masu, discussed here and here)
2. してなければ → してなけりゃ (-eba to -ya contraction, discussed here and here)
3. してなけりゃ → してなきゃ (-erya to -ya contraction, discussed here)

～なければだめ, ～ないとだめ, ～なければいけない and so on are very common double-negative construction. These literally mean "if not then it's not good", but usually you can translate them just as "must" or "have to".

• What does 辞書形＋といけない mean?
• Help me to understand やらなきゃいけない and やらなきゃならない

じゃない at the end adds "..., okay?", "..., right?" or "..., you know?" feeling to the sentence.

• 「～たじゃない」 expression in spoken Japanese

So the whole sentence means "You have to stay calm, okay?", "You must keep quiet, you know?", etc.