YOU ARE NOT DIM! As everyone else has said, a new technique takes practice to master and soon you'll be zipping through the cutout part of quilting like the pro you are or soon will become.
As for the jagged edges of your cut, do you have something UNDER your cutting mat? I USE to store my 6" x 24" ruler UNDER and at the edge of my cutting mat and kept having all these wonky "hiccups" on my cut edge. Took the ruler out from under the mat and sure enough, got a great smooth, straight cut. The 6x24 mat was just thick enough that it made an unever surface for cutting. So, check to see if you have something stored under your cutting mat and if so, remove it.
Around here we can go to our local glass store (windows store) and they will cut ruler templates for us out of heavy hard plastic like is used for the commercial rulers only a bit thicker. They sand the edges and make a pretty decent measuring tool, you just don't get all the measurement lines. If you don't have quilt stores near by this might be something you can do. Several of my quilty friends have gotten ruler templates made for JUST SLIGHTLY LESS than the cost of a commercial ruler template. These work great I'm told.
Good luck!