Case trimmer cutting groove inside my necks!

[Mills]

I own a RCBS trimmer. After I neck size my once fired brass, I'm having trouble with my trimmer guide fitting too tightly into my case. When I trim, I'm getting grooves inside the necks of my cases. It almost seems like my necks are too tight. I'm using the Redding S neck die with steel bushing. Did everything correct on determining correct bushing size, but like I said, when I go to trim, guide is very tight and it's leaving a groove inside the necks. What should I do?

Also, if my cases are longer than the trim to length, but shorter than max case length, should I even trim them at all? Just wanted to have them all the same length.