Abstaining from orgasm for a week or more is one way to get more powerful ejaculations and of more quantity, as is a long, slower session that brings you to the brink and back, to the edge and back etc for a while.
Other methods include massaging the prostate, and performing Kegel muscles to strengthen the PC Muscle. Every day, flex the muscle between your balls and your anus - the muscle you use to stop peeing. Flex it for 10 - 15 times per day for about a second or two each time. Supposedly, this will help strengthen the muscles used in ejacluation.

So they say.

As for size - you're above average for starters, and if your girlfriend is putting pressure on you to change your cock, she's putting too much of the wrong pressure on you. Be proud of what you got, and please her in a whole variety of ways.

Just my thoughts,
CasperTG

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You know, Blackadder, for me socks are like sex. Tons of it about and I never seem to get any.

My Photos:
https://imgur.com/a/80hiRdm