I'm really stressing out

[2sara1]

I can't get myself out of this rut. it's been my day off today and something has happened at work which I know isnt my fault. a customer of mine has bought a car from another dealership and they have messed up on getting the car to us. I rang her last night and explained and she was fine. really nice if anything. and now I have just found out that she has complained. my manager has said not to worry but I feel so anxious and stressed and I can't stop over thinking it i cant help but feel like it's my fault and I could have done something better and that I'm going to get told off for it tomorrow and the worry of getting sacked keeps coming into my mind can someone talk me out of it please