Never trust the time on the box (I'm assuming that this was frozen pizza). The temperature dial on your oven could be off (a lot) - get an oven thermometer if you cook a lot. You should be able to calibrate the dial once you figure out how far it's off.
I usually make mine from scratch. Good pizza requires at least half-assed monitoring, lol. In the first 10 minutes, you have to watch for bubbles in the dough (docking mostly prevents this, but some people don't like docked dough - that's sort of getting picky though) - pop them with a fork/knife or whatever if they appear. Then you're waiting for the cheese to start bubbling, then waiting for the crust to be properly browned.
I like to cook mine on a stone, but that's not the only way. I know a few good dough recipes if you're interested. Extremely easy if you have a mixer, but still pretty easy without one.