Some students do indeed fail the NDB section because they are using inaccurate forecast winds and pre-calculated headings.
They do not fail because the wind is wrong.
They do not fail because their planned heading is wrong.
They fail because they either do not recognise that it is not going the way it should or even if they do recognise the divergence, they are unable to correct the error or worst case - a fail point when tracking to or from the beacon - turn the wrong way trying to correct an error.
What you need to be able to do is orientate yourself so that at any moment in the hold you know where you are and can decide if thet is OK or if a correction needs to be made.
If you fly the hold at 120Kt then here are some rules of thumb;
For every 2Kt of crosswind on the inbound, the drift is 1 degree. Or crosswind/2 is drift.
Calculate the crosswind in the same way (in your head) you do for take-off and landing.
For timing, add 1 second per knot of headwind outbound (subtract for tailwind).
Start watch overhead the beacon and check and reset at the abeam QDM.
Assuming you were on the inbound track at the beacon then - the outbound timing is the same as the time indicated whan passing the abeam QDM.
Always use the 30degree "Gate" to check progress near the end of the outbound.
Finally remember the requirements are to enter the hold in the prescribed manner (remember the entry procedure is based on heading and not track), remain in the holding area and establish on and track the inbound track for a reasonable amount of time. No more and no less.
Use RANT for practice until you can enter and fly any hold using any wind without having to make any pre-calculations.
Aviate, Navigate, Communicate!!
I usually veer - northern hemisphere (back in the upside down half) the surface wind by 20degrees and add on 50%. But your method will be close enough.
Just remember that if the average hold leg is 4nm long or less then a 10 degree error will put you some 0.7 of a nm away from your ideal position. Not too hard to correct for that provided you can use the pointer to a) recognise that there is an error and b) can recognise what correction is required.
Finally remember that you are training to use the IR practically after the test. Be it as a PPL or as a professional pilot. Either case you will never be able to carry enough paper to plan all the possible holds and will not have enough time to plan them pre-flight as a professional.
KISS principle at all times.
Regards,
DFC