Thank you for your reply. Is your employer not receiving copies of billing statements? Given the scrutiny with which you say they examine ever expense, and that it is a corporate card issued for the company, I would be surprised if they didn't get a statement every month. And, if they do, then they already have an idea about you using the card for personal expenses.
Regardless of the amount spent this month, it doesn't change my answer as far as it being unlikely that this would be a good case for criminal prosecution. It may make it more likely for your employer to terminate you, but there still was no INTENT to use the card for fraudulent means or attempt to make the company pay your private expenses. This is supported by the fact that you paid the bill every month and your own statement that the company has a policy of reviewing all business expenses carefully -so it would be silly to try to "get one over" on them. Theft
and fraud require the actual intent to commit a crime. Does this mean you couldn't be arrested? No, but it means that without being able to prove intent, a prosecutor couldn't get a conviction either, and If I were a prosecutor looking at documented proof of regular full payment on the card every month, I would feel like there wasn't a criminal case.
Additionally, in what way would the employer benefit by having your arrested? If they simply want the money back, that wouldn't accomplish that, nor would terminating you. From a business perspective, it makes the most sense for them to arrange a payment plan where monies are deducted from your regular paycheck until paid in full. This may have been a gross mistake and an error in judgment, but you aren't a criminal.
I cannot advise you whether to tell your employer or make the payment and consider this a valuable lesson. But consider that if you cannot make the payment in full, or even if you do, if the employer later finds out what you were doing whether or not it will look worse for you because you didn't come forward.