Arynne is correct, the more you worry about your penis size, the more it will affect your ability to get hard. This is because your conscious mind can only focus on one task at a time - and if you are worrying, then you cannot at the same time be focused on sexually arousing thoughts and feelings which would make you hard.
Although size isn't important to most women - it's more about how you use it - Kegel exercises can be helpful for slightly increasing penis size - and may also help you gain more confidence in your ability to use your penis wisely. Also remember to use lubrication to make entry into her vagina more comfortable for both of you.
I sounds like you are worried about your penis size and this then can lead to performance anxiety erectile dysfunction.
First of all penis sizes vary a great deal but they are all normal. Your penis is normal for you and it is fine, don't worry about it.
Next, to overcome your ED, you will need to take intercourse off the menu and enjoy each other without having the demand to perform. In a few weeks time, when you have a reasonable erection let her come on top of you and do all the work while you just lie there and do nothing. A sense of humor will also help a great deal.
well what size do you have ?
any thing smaller 5 cm is called micro penis. women's vagina has sensitive part of 2" or 5 cm if you have more than that you are small but you are ok, if no then go to doctor. secondly average penis size is between 12 to 15 cm and girt is 6 to 8 cm so if you are in that category you are again ok. penis enlargement is a myth don't fall to this. second thing is that you should be mentally ready for having sex discuss it with your partner too. eat eggs and strawberry and raspberry. it increases zinc and makes you blood flow better and you will get hard and may stay bit longer too but if you still have problem go to your doctor