not stupid at all
Much better you do it than shoot it on the squew...
If you have a spirit level, and a plumb line it's easier to solve, especially if you have a flat area on the gun and an indoor range.
With the walther I put a spirit level across the breech. This I can safely assume is level, it being a german gun. However you can double check by laying it across the top of an open mount as well.
Down range, I put some line (avoid really thick line or wire which can kink) with a lead weight on it and let it settle. (indoor range helps, unless you have some heavy weights)
Once I know the gun is level, (and it wont move), i put the scope in. Looking through it, I align the vertical cross hairs to the plumb line. If you need to move the gun at all, even by a smidge, check the gun is level again.
I also do this on highest mag, because it's easier to see the line and also because barrel distortion is lowest on highest mag, which means the plumb line wont look bent the further towards the edge of the scope's view it is.
I avoid using dovetail mounted spirit levels becaus they don't always sit level. A cheap square edged mini level will do.