That is not how I would check the timing mark. Pull the plugs yes, get a screw in stop that goes through the spark plug hole. Try to set it as close to TDC as easily possible by the mark you have now or close it really doesn't have to be perfect.
When you have the piston up against the stop make a mark on the balancer where the pointer is. Rotate the motor backwards to the stop and make another mark where the pointer is on the balancer. The middle point between these two marks is exact TDC.
This is just my 2 cents.
Curtis