I just bought a used bolt gun, and mounted a scope last night.  The scope cants off to the right about 5 or 10 degeees from the barrel.

Am I screwed or can this problem be fixed?

It can be fixed.  You may need new mounts, though.  What kind of mounts do you have and what kind of gun is it?  I know for ones with a Weaver style rail, Millet makes some mounts where you can tighten the sides unevenly to move the front/rear of the scope to get rid of that difference.  Alternatively, many scope mounts specifically for the gun will have a dovetail front base, and a rear base that will allow you to tighten the two sides unevenly to cause the rear of the scope to be pushed off center.

Putting uneven pressure on the scope tube can cause it to break.

Take your gun to a gunsmith and have him drill new mounting holes that are aligned properly with the bore.

Mounts like the Redfield or Leupold have a great deal of adjustment.  The front mount has a swivel built into the mount.  The rear mount has screws that adjust for windage.  This simply causes the scope to swivel on the front mounts pivot.  Weaver mounts have their strengths, but adjustability is not one of them.  What type of mounts are you using?  Watch-Six

Gun is a Sendero in 300 mag.  -- its used, and I am guessing it is a few years old.

Mounts are IOR weaver type two piece.  Rings are Leupold QRW.

Sounds like new rings and mounts are in order unless I get the gun re-drilled.

Wahhhhhhhhhhhhhhhh [>(]

Sorry, but that sounds like it.  Remington should have done a passable job on aligning and drilling the holes, but I have certainly seen them be less than perfect.  A really dumb off the wall question:  You don't have one mount or one ring on backwards do you?  I have seen some goofy results when some putz really goofs up.  Good luck.  Watch-Six