Why cant i get an like i used to wile watching , im scared now because im a virgin?.?

Ok im a virgin and im 18, ive been watching sense i was 13. the problem is i cant get an like i was used to from a year ago, its just does not get me hard anymore. The only way i can get hard is to rub it but even then it wont get fully hard. im afraid now, because when it comes time to aculy having witch im planning to with a partner in a month, am i gonna be bale to follow through or will i just sit there soft and not able to have ??