This is embarrassing but tips for being on top

I'm 21 years old and Im not extremely experienced but I don't want to show it.
I want desperately to not be afraid of being on top! 
So ladies please save me! I know this is tmi topic but after watching p*rn and seeing this girls bouncing up and down at record speeds is all I have, and I just can't do that for more than 2 minutes. 
I'm getting older I would like to know what could increase and better my sex life now and in the future!