[TxCajun]

Is it in the rail of the aluminum frame or the slide?  Are you certain it is not just in the surface (anodizing)?  How long is it?  What thickness?  A good pic would be very helpful.  If it is tiny and doesn't increase, it is probably not an emergency.  Just keep an eye on it and see if it gets worse.  At some point, you may have to send it back but that depends on how serious it is and whether or not it gets worse. I assume the gun ran fine?  With no pic that is very difficult to judge.

 

[TxCajun]

It doesn't sound like a problem and it may have developed over time. Generally speaking, you do not want to file or sand on the aluminum frame rails as it will remove the anodizing. However, when that is already worn, it can be ok to smooth burrs and rough spots very carefully with some 400 - 800 grit. However, at this point, it doesn't sound like you need to, since the blemish is so small. Just keep an eye on it. It is probably a non-issue in terms of function.