Did riding the slide with your thumb cause a failure to go into battery? That's a little different than a failure to feed, which is a bigger problem usually not as easy to fix.
Checking one's grip on a new gun with dry fire/snap caps at home is always wise before going to the range, especially with a smaller than familiar gun.
I really abhor taking a new gun to the range and having it gack in any way. The loss of confidence in the gun/ammo takes away from the pleasure, then there's the time and effort to diagnose and cure the problem.
I spend less time with problems by familiarizing myself with the gun at home first, and breaking it in the close equivalent of about 500 rounds shot. They are smooth and friction free (reduced) before ever firing a round. Yes, I have a modicum of patience.
I strip and thoroughly clean all parts. I polish all mating surfaces with some 800 or 1000 grit wet dry sandpaper. This includes slide rails, breech face, feed ramp, chamber, barrel lugs, barrel hood locking surfaces. I usually polish trigger components when I know how to get to them (500 dry fire trigger pulls can accomplish close to the same results). I polish the inside of the barrel to smooth it out for less fouling and easier cleaning. I eliminate sharp edges, like the extractor and ejector. If there is a striker plunger safety I polish that and the tunnel within which it rides.
I clean everything again, apply a film of grease because it stays in place. Then I run two sessions of dry fires of about 150 each with full slide action, using dummies once in a while (while watching TV). I leave the slide locked back when not using the gun to condition the recoil springs. I leave the mags fully loaded to condition their springs.
Finally, 5-7 days after getting the gun, I go for live fire. The last 13 handguns on which I have followed this procedure have had no problems—first time or 20th or 100th.
The 3-4 hours it takes me to do this is part of my bonding with the new gun, and it so far has been a guarantee I will not run into problems when I shoot it.
Having experienced problems with many new guns like Sigs, ParaOrdnance, KelTec, AR's, I know today's mass manufacturing methods and QC are not sufficient to produce 100% functional guns every time. I can feel the grit, machine and tooling marks and friction in a new mass produced gun. I fix that.
Sure you can shoot 400 rounds through it and it will gradually improve to where you want it, but the expense in time and ammo will still not produce as smooth or reliable a gun as a polished one—from the first shot, with much less expense.
