Do not worry about the size, I think it is within the limits of average. Moreover, it is possible that the growth of our body parts (including penis) continues until 18-21 years. You are not likely to have any sexual problems or relationship issues because of your size, just try not to focus your mind on it too much because the psychological problems related to our body image issues and sizes can be more damaging for our sexual life.
I wouldn't worry about what u think is small that actually falls into a range of norm. And there is other forms of stimulation that help also like oral sex. Some women dont like bigger guys cause it hurts and feels as if your hitting the cervic. they prefer wider and there's a trick u can do a hoolahoop motion while having sex that might be very stimulating for a women :)