You can choose the size of the map via the "Tags" dialog but there are only three predefined sizes: "small", "medium" and "large". "Small" maps are significantly larger than what you need (smt.h around 10x10 hexes).
In the next update I'm planning to add the ability to request a map of specific dimensions. The goal is to make it possible to generate non-square maps and maps larger than current "large" one, but it could be useful for generating ver small maps as well :)