Yes, I imagine 3" would be a challenge to figure, but I didn't even consider that. Everyone agreed that a spherical mirror would be fine for this one -- training for the future, as I said.

It still isn't much of a scope, but I must say it's better now that I've taken it apart and painted the inside with flat black spray and also trimmed and painted all the bolts and the bottom part of the focuser (the focuser was made from a pvc coupling and it stuck out into the light path). And I also collimated it very carefully. I painted the outside of the tube, and it even looks pretty good.

Thanks for your advice on the pvc tubes. I might try another one just to be "different" (or not so different, apparently). But not if I decide to go 10+ inches as everybody seems to advise! I was just thinking something small for the equatorial mount I'm building.