Looks like you are off to a good start, Mkotch ... your blocks look great. Nice choice of fabrics, good contrast.
Though I had planned to start a My Small World this Fall, I have to admit that the frustration involved with trying to make accurately sized blocks is enough to discourage me. I hate that! When it is the complaint from several quilters (and I am hearing this complaint a lot in regards to the My Small World pattern), one has to assume that the designer of the pattern who is to blame.
Have you tried making slightly oversized blocks and then trimming them down to 2.5" square? Search the Deb Turner trimming rulers and technique sheet for more info on her line of rulers that are designed to be used that way. i hope this helps you.