Please apply 4-5 more times, and see if your scalp develops a tolerance for Minoxidil.
If not, it means that your skin has a sensitivity to Minoxidil product itself, and there is very little you can do about that.
Try to find a hair serum that has no Minoxidil in it.
P.S. 90% of itchiness customers will develop a resistance and will be ok after few uses.