The way I machine stitch a binding is to sew the doubled binding on the front side with a 1/4" seam. (I cut my bindings 2.5", btw...) Then I start near a corner and turn the corner first, to get it nice. I use a lot of pins, and pin the binding from the front, as that is the side I will be stitching from. I work out from the corners and turn and pin the binding every 6" or so. I look on the back and get the binding just past the first stitching line, hold it there, and then pin it from the front. My aim will be to catch just the least bit of the binding on the back-- not miss it, nor catch too much and have a "flap" sticking out. After pinning all the way around, making sure to pin the edge of the binding just over the first stitching line, I start stitching in the ditch from the front. I actually pull the front binding fabric back from the seam, so it will later relax back over the stitching and hide it. I use my eye judgement on how wide the binding should look from the front, plus feeling where the edge is with my fingers, as well as sometimes peeking to see where that edge is on the back. This is finesse... you get the feel for it and it gets better the more you do it. I usually have to go and pick a few spots where I missed the edge, or caught too much... no big deal. I don't think I've ever done one yet that I didn't have to pick a few spots and try again. Keep practicing. Good luck!