I needed to use some flat washers once to space a pressure plate away from a flywheel so that the clutch plate I had had rebuilt would work. They needed to be very close in thickness to work. I went through a box of 100 with a caliper before I found 6 close enough.
Along straight edge across the wheels will tell you if they in-line. If they are in-line you might have a bad bearing, worn tires, or a bad blade. The tension could also be off. If you haven't watched the Alex Snodgrass video on you tube about how to set the blade up, you should watch it now. That might help you solve your problem too.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.