Actually loose powder will clump together a little when compressed in a the breech. After all, how do you think they make pellets. The main thing is, when you moved the clump between your fingers did it return to grains.. It sounds like it did. I am going to guess that that load would have shot just fine.

Besides with the red primer jacket in place all day, and the cling wrap over the muzzle, you did it all right. I would have bet the farm had you pulled the trigger it would have made a great big boom..