It looks so simple in youtube videos, i tried to remove the nub with sanding sponge, from low to high (400-1000), but still i can never make the nub really gone. I also followed the way to cut the parts from sprue, with 2 kinds of nipper, the double edge and single blade to get the part as clean as possible. Yet i still can’t manage to get a clean parts.

I’m seriously confused, what did i do wrong?? I was so frustrated, i spent a lot of time trying to get rid of these nubs yet most of them are still visible.