hung: You raise an interesting and normal question. You can be sure that masturbation will not affect your penis growth. You are of the normal age for this to happen. You are well above average; but be sure that you need not fear being too large/long. Masturbation is normal and healthy. If you have not already found it, try:
jackinworld.com

This site helps answer a lot of questions.

Now for your question concerning future growth and proper attitude. You will grown to what you should be. While this may be an embarrasing situation for you at this time, please be aware that as your body matures the rest of your development will compensate for what you may think is abnormal for your penis size at this time.

Additionally, your peers will most likely be envious of you. Their time will come along also. Be happy with your situation and be thankful that you are developing with out health problems.