ZP, please don’t use your comparison to others in the size department as something to be depressed about. My wife told me about an incident she had when she was younger with a guy who was just too big and how she not only didn’t enjoy it, but after that made sure that the guys she was with weren’t too big. She had one long-term relationship with a man who was larger than I am, but most of them were the same or smaller, and fully erect I was only one half an inch longer than you are now. She never complained about the smaller guys, but was wary of big ones from that time forward. So by all means don’t let your size keep you from having sex. Develop your sexual skills to become a better lover, and the only way to do that is to study and practice.
All that being said, I believe you can easily make some worthwhile gains by using the newbie routine. Practice faithfully but DON’T OVERDO IT! Injury will set back your progress. Be patient and get plenty of rest. Good luck!