How can I ensure that my pizza is properly cooked?
Get a pizza stone. It is important to preheat the stone with the oven. Put it in the oven before you begin to preheat, if your not in a hurry...let the stone and the oven hold at temperature for a while before you put the pizza on it. The stone will radiate heat into your dough evenly. Stones are 'better' than metal (like a cookie sheet) because they release the heat into the dough 'more evenly' If you have a 'pizza pan' putting that on the stone will work well also. 
Completely preheat your oven. Many electric ovens use the broiler coil (on top) to heat the oven to the desired temperature faster, if you attempt to bake your pizza during the pre-heat stage the top is likely to cook faster than the dough. You may eyeball your pizza as done because the top 'looks' ready, when the dough is not yet finished. 
One of the common culprits in an 'underdone' middle is that liquid has soaked into the dough causing it to cook more slowly. If your sauce is too thin you might want to thicken it up some. Also, spreading a thin coat of soft (not melted) butter over the top will form a barrier to prevent the liquid in the sauce from soaking in. Finally, you might try putting the grated cheese on first and then spreading the sauce over that. As the cheese melts and the sauce warms it will settle into (approximately) the expected layers, but if the sauce has been kept from the dough for a few minutes it will not soak in as much. 




If you aren't satisfied with these results then you might try:


Get an oven thermometer. The temperature actually in your oven will vary from 'the dial'. It's expected, just know what you're actually getting. You want your oven to be 'very hot' (professional pizza ovens will range from 600°F - 900°F) your home oven is unlikely to get 'that' hot but 450°F should be close enough to do the job. 
As a last resort... par bake the crust. Put the un-covered crust in the oven for a few (5ish) minutes first, pull it, then top it and return it to the oven.


I hope you find something here to help with your pizza woes.