Fish, everyone is right about the bur. You may have deformed the shaft some also. If you have a "Good" tubing cutter, it will have a triangle shape knife, deburring tool in the handle.
I have used round file, diamond hone rod and such. You don't need to buy a tool, if you have a metal file for sharpening broadheads, it will work perfect! Just insert, the metal handle into the shaft and ream the tube! Also when you heat it up some the aluminum will expand some.
Tube cutters work great, just remember to go slow and tighten the wheels a little bit at a turn.