Drift correction in three numbers
Speed, set and rate are enough to hold a track, if you recompute at every headland.
Heading is not track
The moment a current crosses your leg, the direction the boat points and the direction it travels stop being the same. The gap is the drift angle, and it grows with the current rate relative to your speed. At three knots through water and one knot of cross current, the angle is already close to twenty degrees.
Sketch before you solve
Draw the vector triangle on the deck card: boat speed along the heading, current rate along its set, and the desired track as the direction of the resultant. Solving it numerically is fine, but the sketch is what tells you when the answer is impossible because the current is simply faster than the boat.
Recompute at boundaries
A single correction for a whole leg assumes the current is constant. Around a headland it is not, and the error accumulates on whichever sector you skipped. Split the leg at every place the pilot book gives a different offset, and carry a correction for each.
When the answer is a re-time
If the required heading would put you outside the planned corridor, or the drift angle passes twenty degrees, the correction is not a heading but a later departure. Change the plan, not the compass.