A few bits and bobs for you to remember.
- You are not done growing. Boys don't finish puberty until about 21
- Learn how best to use it. In penetrative sex there are positions that will feel like they hit better spots and go deeper. Ask her what she likes.
- Don't get fat. Fat deposits at the base of the penis can make the usable length and visible length of the penis smaller. I can provide anecdotal evidence, but I shouldn't.