Hi I’m 25 years old and my girlfriend is 20 years old. We do sex last 3 months but when I am going to sex with her I can't satisfy her. So how I can satisfy her because of my penis size. Secondly when I’m going to sex with her I’m feeling nervous and scared

Get this book, and experiment until you find what works.

Amazon.com: The Joy of Sex: Fully Revised & Completely Updated for the 21st Century (9781400046140): Alex Comfort: Books (http://www.amazon.com/The-Joy-Sex-Revised-Completely/dp/1400046149)