'n' is the single hump cousin of 'm'. The mistake is almost always drawing one hump too many. The fix is rhythm. Say the sound out loud: 'nnn' is one steady note. Now say 'mmm', your lips press twice. The hand follows what the mouth does. Practising 'n' and 'm' alternately on the same page builds the difference into muscle memory.

One hump is enough. 'n' does not need two to do its work. Confidence is knowing when to stop.