Jon Pop started at 4.75" BPEL and PE'd until he was 8.5" BPEL (I'm not sure whether those numbers are exactly correct), overall though I hear he gained around 4". Don't worry, there's plenty of hope. Even if you gain 1" or 2", PE is worth it! Any gains are good gains.
We aren't all American's mate
And not all American's have 6 or 7 inch dicks either, there are a few statistical threads you could check out, batwoman has one stickied somewhere
Just remember that you are better than the people who tease you, teasing based on stereotypes is pretty low. Start doing PE and gain the confidence to stand up to them.