Trust me, from personal experience, if you actually had a growth disorder you'd know about it.
You'd find it ridiculously hard to gain any muscle and maintain fitness, you would probably have to have a nap after school from sheer exhaustion, you would be the smallest in your year by not just a few centimetres, 4 inches.
Mine was diagnosed so now I have injections. But even so, 4ft 8 to 5 ft 1 (but still growing i guess) is still pretty sh*t.
You have nothing to worry about, if the person you like doesn't want to go out with you because your small, personally, I think your too good for them anyway.