Please help

a few days ago my friends and I were in a clothes shop (not saying which one but a major retailer), and I tried on a necklace in front of the mirrors they have in the accessories section. Then I picked out an outfit, tried it out in the fitting rooms, bought the outfit and left. The beeper didn't go off but I accidentally left my original necklace there and was still wearing the necklace from the store. the necklace was 3-4£ I think. This was a genuine mistake and I'm worried they will be able to look at the cctv footage, see me trying on the necklace and track my card down from the purchase I made. What is going to happen to me? will the police get involved? will i get a fine? should i go back and return the necklace or will that just make things worse.
if there is no evidence of me leaving the store with their goods can they technically do anything?
im not under 18 btw
please help
thank you

Just go back and explain the mistake. No actual thief would return with stolen goods so they'd probably believe you. Depends on how long it's been tbh

Hey! i think youll be fine dont stress... some people fully walk out of shops with loads of stuff under their jackets or in their bags. They wont chase you up over £3-4!!