The figures you've used are close enough to work out in the real world. As you turn, the way the wind affects your track will change, so it's never going to be exact. All of these methods just have to be close enough than when you look up you see the reference point you're expecting and go from there.
There are plenty of tips and tricks out there. I prefer to mark halfway points, when you get there see how far off track you are in degrees, double the error and that takes you straight to the destination. This works out as less track miles flown, but the method you've stated has the benefit of getting you back on the line you drew on the map early on, so a feature you were expecting on the left/right should be on the same side.
Another good tip is that while you're in the planning stage with the wind, magnetic variation, and any compass deviation, always round the error the same way, that way when you're off track you know which side of track you expect to be and how you should therefore be correcting it.