I asked a girl sitting opposite me in a club if she was single she said no that was it. I’m so paranoid now that I’m in trouble what to do ?
You need to stop being so mental. You asked a question , she answered it, the end.
In trouble about what? You checked if she was single, she told you she wasn't, and neither of you continued the conversation. You're not any more in trouble for asking than she is for answering.
Youre paranoid her boyfriend/girlfriend will beat you up? Asking is someone is single wont cause a conflict. Youre good.