I picked up an new 637-2 over the weekend, I was doing some dry-fire exercises with it, after about 20, it locked up tight.

After opening it up, I found the cylinder latch spring was sitting wrong, and the IL flag spring wasn't in it's groove, it was sitting between the flag and the frame. Not sure which was the problem, but I corrected those and reassemble it (should have left out the flag, but I digress). Works great DF, I haven't had it to the range yet.

When looking in through the hammer slot I noticed a ding on the frame where it meets the side plate.

I own better than half a dozen Smiths, mostly J's & a K. I've had them all open from time to time and not had this issue.

When I removed the hammer I was careful to keep it in the correct position so I wouldn't ding anything coming out or going in. I cycled the action manually prior to putting in the hammer spring, after the hammer spring, I cycled it one time holding the hammer with my thumb to release it without 'slamming'.

It's only cosmetic, but I really hate the fact that I screwed up a new piece.

Any idea what I may have done wrong ? or just roll your eyes and call me Bubba

Some pics

Looks like it was dry fired with the side plate off allowing the hammer to move a bit to the right.
Ask me how I know.

__________________
Dance like no one is watching.

Yep - all indications your gun was dry fired with the sideplate off and the hammer was not seated properly. Maybe you can touch it up with a fine file.

Thanks, I believe you're both correct.

When I took off the side plate, I pulled the trigger to see where it was binding and it cycled the hammer, to my surprise.

Lesson learned.

Thanks

For me too. I have had all my S&W's apart sometime during their life and so far haven't had the bad luck you did. But I will remember your experience!

The good news is that other than cosmetics, performance and integrity will be unaffected. You are the only one that will notice it unless you point it out to people.

Agree with Ken on dressing it up with file but I'd personally remove the hammer and then put sideplate back on.
If you do it with the sideplate off you may end up with a bigger issue
Use a fine, jewelers file