Foreskin dosent pass the head when erect but fine when flaccid. should i stretch it by myself or see a doctor? but scared to see a doctor as i am worried i will get an erection/boner. dont know what to do?

Do not force the foreskin back. See a doctor for a proper treatment. Visit this site for information and talk to your doctor: https://www.ncbi.nlm.nih.gov/books/NBK326433/#:~:text=There%20are%20three%20treatment%20options,remove%20the%20foreskin%20(circumcision).

Using a small amt of cortisone as lubricant gently pull back foreskin as far back as possible several times a day. Gradually the skin will become supple. Good luck