There is erectile tissue in your penis. When the tissue is strong your erection will be strong. When it's weak, you're erection will be weak. Try pushing the shaft of your erect penis down into the pelvic area (where it came from.) Yank it hard, push it in hard. It may be a little painful to do this but pain will subside after you've consistently man-handled your unit for a period of maybe two weeks or more.
This helped me develop a large and strong penis I went from 6" to 7"+! Also, practice tightening your butt muscles-pelvic floor, and notice your testicle sack move when you are doing it right. This too will help develop the erectile tissue in your penis and the length will follow. It takes time though and I don't recommend porn when you do this. Sexuality is a beautiful thing!
4 1/3 soft