What should you do if your big sister dresses you up like a girl and takes you into public even if nobody could tell it was you and you cant tell your parents?

If nobody knew it was you, and you know you're not a girl, then you shouldn't worry too much. Tell your big sister that if she does it again you WILL tell your parents. Your sister is maybe threatening you, but if you are serious then she should back off.

If she doesn't back off and you can't talk to your folks, then talk to a trusted adult. This feels to me like sexual abuse.