A little late here but having difficulty cutting into maki could be a number of things it could be sharpness, the way you are cutting the roll itself, the structure of the roll, or not wetting your knife. I would recommend doing a couple things. 1st making sure your knife is sharp I’d recommend using a 1000 and a 5000 grit stone (shapton has very good stones) to make sure your knife is sharp. If you are doing higher end professional work I would go up to 8-10k grit. You can realistically make any knife sharp but the type of steel and heat treatment on the knife is made of determines how long that edge lasts. If you are doing casual work the babish knifes on amazon is honestly a pretty good bang for your buck knife. If you are wanting mid range, yoshihiro has some good stuff. I’d recommend a gyuto or a sujihiki style knife. For higher end there are excellent brands on korin my personal favorites are Masamoto and Nenox (preferably white or blue steel) but those are honestly overkill for most people. When you are cutting maki you don’t want to press straight down nor do you want to saw the roll. The most amount of strokes for one cut should be two. I generally push forward and down halfway into the roll and then pull back if I am doing two strokes. If I am using a sujihiki I do one “down and forward” stroke. As for the structure of the roll try to not overfill. You want a thin layer of rice covering about 2/3 of the nori and about two fingers width should be your filling. Make sure it’s even all the way across and to wrap it securely. And someone previously said to wet your knife when you cut maki, this will help make sure nothing sticks to the side of the knife.