I used the NOVUS 3 and 2 on my Nauticam acrylic ports several times now.
You won't be able to remove huge scratches with it. Consider to start directly with 3 and then 2. Repeat the procedure four or five times. Wash with water between each step to remove Novus and to check how it is going on.
Even if you do not remove completely the scratches they will be invisible underwater.