First offence shoplifting - what punishment should I expect?

I've been caught shoplifting from asda. I'm not going to lie. I meant to take the top and shoes which came to roughly £20. I don't know why I did this bit I did. The rest was purely accidental. The totally came to £28. I've never been in trouble with the police in my life. I'm a 31 years old female who works as a carer 

They went through my shopping and bag and found things I hadn't paid for. They had checked cctv for what soles I went down on and realised certain things I hadn't stolen at all even though they tried. The police officer then asked me to come down the station tomorrow for an interview. I'm petrified. What going to happen to me?