I can I act like Im smart?

Kso, I was always a straight A student until I got to grade 7. My grades started to get bad but there were nothing less than a b-. but half way through my first semester my mom took my to this guy and I had to take an IQ test and testing for stuff like ADD and all that other stuff. But my IQ was really high and he said that I didn't have nay sort of disorder. He told my mom to take the papers we got back from him to this other guy and he was like a psychiatrist or something. and he said that when I got to middle school and acted all smart and stuff that no one ever knew what I was talking about so to "fit in" I dumbed myself down to there level and that effected my grades. and my parents were really mad at me for my grades so I want to start acting smart again. but acting stupid is just natural now and I don't even realize when I say something stupid until after. So I need tips to lose the habit of being dumb and get into a new habit of being smart again. Pleeease!! Thanks in advance.