Minz is likely right. I don't use the flat of my hive tool to notch, I use the corner, and it takes out about three cells so I squish the larvae in the two adjacent cells to make sure I don't get two Q Cells tied together. This allows me to notch more places spaced apart for easier cutting later. About two thirds of the way down the cell wall and flatten the cells below the one you notched well.
Bad eyes, so I use a magnifying glass, look along the eggs until you find where they have just hatched, the new Larvae will actually be smaller than the egg. You probably know that already, just saying...
Try punching sometime. You might have better luck. It sort of forces you to slow down and choose carefully.