Dear civathebully,
You told that your penis is 13cm which is quiet good, so i assume your testicles will too. You are worried too much that's why your erection is not normal. Observe when you are naturally excited or eager to have sex. Here you have'nt mentioned your information so we can't explain much here. But from your sense i think you are unmarried and have a habit of masturbation and watch lot of porn, so you feel that your tool is small. But don't worry its normal so live a healthy life. Everything will be okay and if then you find somrthing wrong then go to the doctor.
You told that your penis is 13cm which is quiet good, so i assume your testicles will too. You are worried too much that's why your erection is not normal. Observe when you are naturally excited or eager to have sex. Here you have'nt mentioned your information so we can't explain much here. But from your sense i think you are unmarried and have a habit of masturbation and watch lot of porn, so you feel that your tool is small. But don't worry its normal so live a healthy life. Everything will be okay and if then you find somrthing wrong then go to the doctor.