Your saw blade could be heating up and if so it could distort some while cutting.

I use a tool shaped like a triangle but it's called a "speed square" to check my blade to my saw sole plate. And I check the blade between the teeth because if the speed triangle hits the tooth it will not be square.

With working with power tools and large timbers it may be necessary to still straighten out a joint with a chisel.

Good luck with your project.

Jim Rogers