I made it 17.7 degrees left (nearly).
(12 deg off heading at the waypoint, 6 deg more to turn to destination.)
Similar triangles seems to mean you are 2 nm off track to the right with a baseline of 10nm, so your deviation is (90-(tan-1 10/2) ) deg.
You are 2nmright with 20 to go so you need a further (tan-1 2/20) degrees left.
My , its a long time since I did trig so this could be complete pants...
(edited to justify my answer<G>)
(again to correct duff typing)