Phil, you've done a good job of assembly. One thing I would recommend tho., & that is to reverse the finder base plate 180 degrees, so, as you mentioned, the finder will not slide off. (downwards). I think you'll find it has a 'moulded stopper' @ one end. From the couple of t'scopes that I've seen, most come 'wrongly' mounted. imho.
As Mike says, don't worry too much about the dings.
Collimation is easy, really it is......
http://skyandtelescope.com/printable...rticle_790.asp
http://www.andysshotglass.com/Collimating.html
HTH.
L.