Im 21 years old and feel like I am mentally slow at times in real life doing simply things I get brain freezes?

and or confusion. I took a iq test in elementary school and my iq was beyond amazing it was a whopping 81 (sarcasm). I never pay attention in class because I feel like Im not going to understand anything anyways so I zone out. Alot of times when I pay attention I understand things quick but my memory seems terrible and doing certain things mentally I am really slow at it. What do you think guys? What should I do?