want to have sex with girl but cant able to do

many time my girlsfrnd has insist me to have intercourse with her but due to fear of gettin thing worsed i never did any such activity ever, i dont know i m confuse while doin act rather then step away from thier but now one of my girlfrnd hav told me that u dose suit me atall, i need help should i go to do such act or should i wait for sum time bu the way i m now 25 yrs old guy

u can also personnaly replay me in my email id - _[removed]_.