What will happen if a person is injected triamcinolone acetonide with xylocaine (lidocaine) even if they don't have any scar tissue problem?

As far: The shot is indicated and the technique is correct, you should be safe. Sometimes the steroid could cause fat atrophy, specially if given too superficial.

Skin thinning: Results will vary from no side effect all the way up to focal skin ulceration. The more dilute the triamcinolone the less likely one is to have a side effect such as skin color change (reddish-purple), skin atrophy(thinning) and/or skin erosion/ulceration. All of these side effects are unlikely and are often temporary even if they do occur; if they do then seek a dermatologists care.

Not much: If there is nothing to treat nothing will happen except the area will feel numb.