I recently purchased what I consider a really nice Garand for my son.  (It is his present for earning his Eagle Scout rank).  We shot it this past weekend. It was awsome! - We were both grinning the entire time.  We field stripped it to clean and lubricate it a couple of nights ago.  During reassembly, I dropped the op-rod on the concrete garage floor.  Of course, it landed right on the edge of the gas piston at about the 10-11 o'clock position (with the rifle upside down and looking at the face of the piston).  I have inserted a couple of pictures below.  This is our first Garand so we are learning.
How bad did I mess up?
Is there anyway to clean this up and continue to use it without damaging the bore of the gas tube?
Is it possible to replace just the piston or do I need a whole new op-rod?
I'm not normally this clumsy.  As we saw it start to fall, we both made a grab for it - and we both missed.  
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It’s fine

Just smooth/polish the banged edge with some fine grit sandpaper (400 - 800 will work) and it’ll be good to go.

This is all I would do

Smooth it out and you'll be good to go.

Should you ever mess it up worse than that and require a replacement piston or other op rod work, Columbus Machine Works can fix op-rods.
http://www.columbusmachine.com/oprod.htm

Thanks for all the replies. Sounds like I didn't damage it that bad.  
I'll hit it lightly with some really fine sandpaper and reassemble.

Thanks again!

Plus, it ain't nothing that Mike Stacey @ Columbus Machine Works can't fix. He's the go-to guy for fixing or rehabbing worn, outta spec, or damaged op rods.

Both S.A. and F.A. use his services, although it would take the judicious use of pliers and a blow torch for a couple of days before they'd admit that 'on the record.'

I'm going to disagree on the files/sandpaper.  Get a couple of fine stones and light oil, darken the damaged area with a sharpie and carefully blend in the damaged area until it is level with the adjoining surface.  

Failing that, you can silver solder in a new piston.  They are cheap.

Op Rod Piston

I would not sand or stone the piston. Leave it alone as is

Leave it alone.  


And if you pm me, I will send you a replacement piston tip.

Shoot it, if it gets worse, fix it as above.

Hking

If you have a wire wheel on a grinder I would just lightly remove any raised areas on the gas piston. You aren't trying to change any dimensions, just knock off any burrs.

If you don't feel any sort of drag when assembling, I wouldn't really worry about it.

Thanks!  Based on what I've read, it sounds like the replacement of the gas piston on a Garand is probably beyond my tools and skill level.  
I did clean it up VERY carefully with some 1500 grit sand paper.  Just enough to knock down the high spots as observed under a magnifying glass.  A few drops of gun oil and checked the fit and movement within the gas tube.  Smooth as silk. I believe its' GTG now.  

Thanks again for all the responses!