AMMorgan ... Good for you for trooping on, despite your difficulties!!!
My first thoughts are green painter's tape to the rescue!
What I'm thinking is that maybe you could get your stripset in place across your cutting board, and then be able to cut several squares before having to realign. Maybe use smaller pieces of the tape, so that you can keep aligning with the cutting board line as you go, til it's in place across the cutting board. Bonus! you don't have to worry about where the painter's tape is, as you can safely cut through it.
Some have found that putting a weight (gym hand weight? or something hefty) on top of the ruler, once you have it in place, helps stabilize everything as you cut. With the hand weight, you can grasp it, and lean on it, as you cut.
These ideas may not solve your problems ... but maybe they can help a wee bit?
Otherwise, I'm sure others will soon be here with more ideas for you!
Good Luck!! and keep up the spirit!!