Timid when applying relaxer

   I am sooo sooo timid when i apply my relaxer,, i do
it now about evry 4 to 5mths,, but i apply too little
becuz Im afraid to overlap,, I had a horrible
experience when my hairdresser overlapped over
and over again and the entire front of my extremely
thick curly hair was just about half an inch long on
the left side!! and breaking from near the root
everywhere else,, Now when i relax i use alot of
preconditioner to prevent dreaded over processing ,,
ieven use it on the hair im relaxing!!!
        Im hair obsessed!