You are just a kid. Don't worry about penis size. When you hit 18-23 and the highest levels of T hit your bloodstream your penis may grow larger. I'd venture to say most guys here thought they were small at your age.
1. Most women I've been with have been more intrigued/worried by the girth rather than the length. Many vaginas are not very deep. And if you beat the hell out of her cervix with a dick like a billy-club you can hurt her. Now, anal, that may be a different story.
2. Learn about how to please a woman. Learn about her E zones, learn where on her skin to kiss to make her go goosebumps, learn that your saliva followed by your breath can drive her nuts, learn if she's a 'look in my eyes' girl or a 'talk dirty to me' girl. Listen. Engage. Make her feel special. Learn how to please her orally; many women are clitorally orgasmic and not vaginally orgasmic. Stick a Louisville Slugger up some chicks and it ain't gonna hit the button. If you are GOOD at oral and those other things, and you get her to the brink 10 times and pull her back, she's going to pop like a geyser when you put a finger in her, let alone 5" of dick.
3. People can only make fun of us if we allow them to make fun of us. If you ignore it, be above it, act like its untrue, most folks will think its untrue. OR - just say it wasn't you, she's loose like an un-stuffed turkey.
Have fun, don't worry, at 16 you have many years full of crap to worry about that are better than this.
Who knows, at 25 you may be swinging hardware like Mr. Goodwrench.