first of all u need to be calm .
sex involve not only genital but whole body
its control is in our brain 's hand
so u have sound mind and clear thought while sex
are enemies of sex
they interfere with each stage of sex
so u must be positive in matter of sex ,keep ur negative thoughts out side ur brain
i know it is difficult initially ,but once u learn ,u will do better and better.
so be relax ,take a deep breath .
better to consult doctor
if u think u need to .