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Yes. You can use Я мог не... (and as you're a girl as I take it then you'd better say Я могла не...) For example: Я мог не идти туда - I didn't have to go there. But mind "I didn't have to go there...

You must not do that = (Вам, тебе) нельзя этого делать.
You don't have to do that = (Вам, тебе) не нужно этого делать
You shouldnt' do that = (Вам, тебе) не следует этого делать or (Вы, ты) не...