Check with a stick in the cyl, while looking at valve rockers when intake opens and closes fully, u will see the crank mark approaching zero.
If u suspect the mark is wrong then find true tdc on your engibe and mark appropriately. You will need to make a tdc stop with a bolt in spark hole and mark the crank pulley, rotate forward so engine stops by bolt obstruction, mark pulley, then rotate backwards and mark again where the engine stops.
Measure distance between both marks. TDC is exactly in the middle of both marks.