I think my entire family thinks I speak german fluently because I took the classes in high school and then came home and spoke completely made-up gibberish with confidence
Why would you lie to your family like that?
I think it is just funny.
Learning a second language is really good for your brain and useful overall. Maybe you should learn proper German and not your giberrish.
I'm going to take this opportunity to play dumb and say I can't speak german.
You have the responsibility to tell your family the truth. You know German and it was all giberrish.