RE ATC see
CAP 413 Radiotelephony Supplement 3: A Reference Guide to UK Radiotelephony Phraseology for General Aviation Pilots | Publications | About the CAA page 10
Changing Frequency
You will normally be advised by the appropriate ground station to change from
one radio frequency to another in accordance with agreed procedures. In the
absence of such advice, you must notify the ground station before changing
frequency, using the expression ‘changing to’ followed by the name of the next
air traffic services unit. However, pilots flying in controlled airspace must obtain
permission from the controlling authority before changing frequency.
As for getting back on track, there are various ways, but what your are doing sounds very like what I was taught.
A brief glance though, suggests that your numbers aren't quite right. However - this is just a quick glance!
If you are 1/4 of the way down the track:
If you turn 2x track error, you should get back to the track at 1/2 way point. If you then turn to 1x track error, you should then be following the track.
If you are 1/2 way down the track:
If you turn 2x track error, you should get back on track at the end of the track (ie your next waypoint).
The way I think of it, is that if you turn the track error, you will now be travelling parallel to your desired track (which is probably what you should have been on in the first place). If you turn 2x track error, you will move back towards your desired track at the same rate as you left it (so if you have been going wrong for 1/4 of your track, you will be back on track after another 1/4).