Hi Valerie, I feel your pain.
First, I've found that not all cardstock is actually the dimensions they say it is on the label. The paper can be "off" and the measurements not exact. Sometimes it's not you, or the trimmer. It's the paper.
I have a Making Memories cutter and like it a lot. It's the only trimmer I use, so my cuts should be consistent. I line up my paper to the right of the measurement line on the base of my trimmer, so I can see the line. I tend to be a precise person, and I cut with care.
I use white cardstock for my card bases, and have a brand I like from Sam's that says it is 8-1/2 x 11, standard size. So, if I cut it in half, at 5-1/2, I should have 2 card bases the same size. When folded it should be 4-1/4 x 5-1/2, right? Wrong. Usually, one of the pieces turns out to be a tad longer than 5-1/2 after I cut it.
So when I attach my cardfront, 4-1/4 x 5-1/2, which I have carefully cut from another kind of cardstock, invariably part of the white hangs out along the edge of one of the pieces.
I've resigned myself that this happens with different brands of paper, and keep my Cutterbee scissors handy to just trim off the edges.
