you appear to have guilt feeling because your previous masturbation. You must understand first that masturbation is a good thing it does not harm whatsoever. there are lots of wrong idea attached to it. I am a doctor myself and so If you trust me it will do you good but if you do not then it is your choice. For your premature ejaculation ,you may apply Xyocaine gelly ,available at all medical stores ,over your glans penis 20 min before the sex act.It will make the glans numb and ejaculation will be delayed.Do not bother about Big penis and thick penis which many boys boast of .It is the love and foreplay which does the wonders