As has already been pointed out, so long as you're measuring properly you're plenty big (big enough for porn). The sad fact is it won't help you that much. As focused as men get on their size there are plenty of other things that could still make sex suck with you, some are things you can work on but more often two people are just a bad match. e.g. what if you like getting rough, pulling hair + spanking, but she gets downright offended if you do and is immediately turned off? It's nobody's fault, but you won't have a good time. Compared to all those factors, are genital size mismatch is one of the least likely things to be an issue.
Don't talk about your penis at all with girls. At least, not before they've enjoyed yours first and even then only if they've brought it up or there's a really short segue. Many girls, especially the ones with more dating experience, know how obsessed men are with dicks. Even the women who care a lot don't care half as much about your dick as its owner does. Obsessing over your own size will make you sound insecure: either you think you have a big dick but need to focus on that to make up for your other shortcomings, or you think your dick's small and lack confidence. It's a losing scenario either way.
As I often say, telling someone you have a big dick is like telling someone you're famous: it loses a lot of impact if you have to tell them.