@serensurface-- As far as I know, the makisu used for square rolls are made of bamboo sticks that are completely flat. The classic makisu has rounded bamboo sticks and those make round sushi rolls. I suspect that this is what you have.
I actually have a makisu that is multi-purpose because it is flat on one side and round on the other. So I could make different shapes with it but I usually use the round side for typical round sushi.
I suggest getting one like this but please don't pay a lot for it. Sushi rolling mats are very affordable and regardless of what you pay, they all do the same thing. Just make sure to use plastic wrap before each use or you will have lots of trouble during cleanup as the article said.