Welcome from AZ. I gather you did not buy the car new. The 3.8 sticker would not have been placed during production because the plant where Challengers are made only had 3.6, 5.7 and 6.4. So they would not have 3.8 stickers. I suspect it was replaced after the fact maybe after front end damage.
Hello and Welcome from Illinois!.......Stop by or call the FCA dealership parts department. Give them the last eight digits of your VIN number and the part number from the wrong emission sticker (lower right hand corner of the sticker, ending in 111AA). They can cross reference the numbers and order the correct one for your 5.7L. Should be approx: $5.00. Peal off the wrong sticker and put the correct one in its' place.