You really don't have to make pizzas round.
I have always used my Wilton cake pans since I used to do cake decorating so I have a 1/4 sheet size pan and then one that is almost a half sheet pan size. Any pan will work as long as the sides are a little higher. If you own a lasagna pan that would be excellent to use. I don't even own one of those myself though. You could even use a small roasting pan since that has a higher side than a cake pan.