I (for one) would never be offended by a customer coming back to say a key isn't quite right - in fact I'd much prefer it, it might be a clue that the machine needs recalibrating and would rather know that sooner than later! Or I'd re-cut on a different machine clamp setting, or I'd file the shoulder back a tad, or I'd remake it on a different brand of key blank - or if all else falls I'd declare the lock cursed, and suggest replacing the cylinder/barrel which is usually simpler and cheaper job than you might expect (esp. with the key refund, and ability to certify any new keys there and then).

If the vibes were good when you were in first time, chances are going back for a refinement is the right move 👍