Sorry to hear you been treated in such a manner that neither store or police took your role or potentially extenuating circumstances into account, being under pressure / work load / previous history if any.
What i dont get is didnt they offer you a police caution at all, years gone by first offence for specific crimes would just earn you a caution, unless you've got any police history?
Just seems a little unfair , unless cautions dont exist any more, what exactly is a resolution order, a promise not to commit the same offence within the year, else you could be charged for that offence as well?
It may well have been better to force them to arrest you, take you to the nick where you could have got duty brief and cautioned?
Sorry hope things work out