How did you get your fusible interfacing to stick to your block??? I think the normal method is to iron the fusible to the t-shirt fabric, then cut your block. It is the fused interfacing that gives the t-shirt fabric stability. My understanding of interfacing is that it has fusible on one side. That is the side you iron to the fabric. Or did you use a two-sided fusible? I don't think two-sided fusibles are called interfacing, but maybe I am wrong about that.
Edit: I think I'm right about interfacing having fusible on only one side. Here is a Wikipedia article on it:
http://en.wikipedia.org/wiki/Interfacing