It won’t be very accurate if you don’t track both dimensions of motion, especially if you use omni wheels. Having 2 parallel wheels and an inertial sensor doesn’t give you any more information than having 1 tracking wheel and an inertial sensor, so it would be very beneficial to turn one of them sideways if you can fit 2 wheels anyway. If you can truly only measure one direction, you’ll want to use reset points on the field to eliminate any error that’s accumulated during the runtime.