Yes, pizzas means more than one, and pizza's means either "of the pizza" or "pizza is"/"pizza has", e.g.
1. Here are your 77 pizzas. (= plural)
2. My pizza's cold. (= is cold)
3. My pizza's got too many anchovies on top. (= has got)
4. This pizza's provenance is unknown. (= the provenance of this pizza)
Best wishes,
MrP