What do I do if I am not "large enough" for my woman?

I'm not sure short of surgery there is anything you can do. That being said, the old saying it's not the size of the boat but the motion of the ocean that counts! Learn your mate, figure out what it is she enjoys! There are other things way more important involved in sex than just your size!

I think its more of a confidence game there are many ways to satisfy your woman but if you do want to,  you could try male enhancement products which you can buy. Some give a free trial.

I think small, medium, large these are doesn't matter during lovemaking. Your attempt matters very well and how to satisfy your partner and give pleasure moment to her.

The biggest thing that you need to realize is that if you expect girls to only want excessively massive penises, it'll eat your confidence. 5" is the standard, and if you are very good with how you have sex, it shouldn't matter.

I think this is no problem for me.

I have a friend who complained once in our private conversations that he was not very large and could not last long,  his self remedy was to have his wife mount him and use several fingers aligned with his shaft and stimulate her clitoris.  I hope this helps, also while searching for exciting new sex toys online  I have seen slip on shafts that go over the penis and increase both girth and length.

There is no natural way to permanently enlarge it significantly, however:

Testosterone and estrogen are the male and female hormones respectively, they tell your body it's sexual identity according to their scale with each other. 

More testosterone, and your body will align itself with being more masculine. This will lead to increased penis size in men and reduced breast size in women. Alternatively, more estrogen will make the body believe itself to me feminine, hence smaller penis  and larger breasts, even leading to the formation of breasts in men. 

There are shots, surgeries, chemical injections, etc to get more of one or the other, however to be more natural and healthy, it is better to trick your body. Doing things that align with masculinity such as aggressiveness, strength and endurance exercise, and general primal urges lead to the body producing more testosterone.