How to get mental health record expunged?

I have a 302 on my mental health record from 3.5 years ago that is keeping me from getting a rifle to go target shooting with my friends. the 302 was because i was in college and i came home in the middle of the night from parties every few nights and my parents kept getting pissed off at me. they told the doctor i was trying to drink myself to death with is completely untrue. I was in there for 14 days because my parents kept on telling the doctors that i needed to stay there. Now i am denied to get a firearm because my parents were being a$$ holes. what can i do to get this off of my record.