Some good and some not so good advice here. As far as I can see, no one has yet mentioned the easiest way I now of getting back on track, although that may be because many assume that you have already tried it.
Assume first that you are flying a relatively short leg (say 60 nm). Forget the problem of adding up track error and closing angles. Draw a 10 degree drift line BACK FROM YOUR DESTINATION. Now divide the leg into halves or thirds or quarters as the good landmarks dictate.
Once airborne, compare your actual position at one of these divisions with your planned position. Transfer that onto your map and estimate the number of degrees off track by comparing with your 10 degree drift line. Let's say that by the half way point you estimate you are 5 degrees right of track. All you need to do to arrive at destination is invert the fraction and apply that to the calculated error. In this case you are 1/2 way along so you invert the fraction making it 2/1 x 5 degrees = 10 degrees. Therefore you need to alter heading 10 degrees left to arrive at destination.
It works perfectly for any point along the track: 1/3 gone becomes 3/1 x error,
2/3 gone becomes 3/2 x error
1/4 gone becomes 4/1 x error
etc.
This is logical, because if you think about it if you are 5 degrees off after only 1/4 of the total distance you have a large error so you will need a large correction. Conversely if you are 5 degrees off after 3/4 gone you will only need a small correction.
For longer legs you can divide them into half, draw 10 degree error lines from the half way point AND the destination and use the above method to get back on track by the half way point and then treat the second half in the same way. This stops you wandering a long way off in the first half when CAS might be a concern.
Cannot agree more that the 2-3 mile waypoint system is a recipe for disaster. That's not navigation, it's map crawling, and if you are spending that much time looking at the ground and the map you can't be doing much in the way of looking out for other aircraft.