This is the way I make all my T-shirt quilts. Using quilter's grid interfacing, I iron on the cut t-shirts using an applique pressing mat leaving 2 inch strips on all four sides of the t-shirt. Then I iron on my 2 inch sashing inbetween the placed t-shirts, Including the outside borders. Then fold the right sides together and sew along the lines. You end up with perfectly matched points and cornerstones and the t-shirts are stabilized by the grid.
Here is the site I learned from. I am on dial-up and can view this just takes about 5 minutes to load.
http://www.crookednickel.com/memories.html
If you have any questions, please PM me.
Sheila