"Cancel MayDay" will be fine as you must have already set the alarms ringing/pulse racing by screaming Mayday in the first place. Other variants could be a downgrade to PAN instead if the problem is still needing attention, but not critical as first though.
I have had an emergency PAN cancelled on the RT, unfortunately it was a Medical PAN and priority was requested instead for "Humanitarian Grounds" which was duly given anyhow.