Paste the DTM here for us to check. Most likely scenario is as Dan said, you never gave the inner point(s) any tolerance.
Also as he said, if the DTM is used only for checking if you have runes, it's safer and more efficient to check that via the spellbook tab right as you're calling for the spell to be cast, especially if it's a spell that you'll be casting multiple times between banking as the DTM will return true if you have 1 rune, which may not be enough for that spell, or enough for an inventories worth.
I'll paste my rune check function (OSRS), call this right before clicking any spell - each time it's going to be clicked.
Simba Code:
function NoRunes: Boolean;
begin
Result := CountColor(255, MIX1,MIY1,MIX2,MIY2);
end;