well, I had the same problem with the grafting when I did it the other night. I'm sure if you watched the video here and did it again, it'd get easier everytime. I suggest tugging on the yarn a little everytime you move onto the next repeat (ie, after one set of k,p,p,k slipping) and check it to make sure it mimics the surrounding stitches' size. When you graft, you always do it on the outside, not the inside. But when you are doing another technique other than the kitchener stitch, it's different. The mattress stitch is also on the outside, but it's for side seams and it actually includes a seam allowance.
When I did the kitchener stitch I was reading from Stitch n Bitch... It was sooo confusing to me and I watched the video here and it was so clear to me. I just had to watch it over and over until I got it and then I went and finished it up.