Schools generally request final sets all transcripts be provided prior to your start date, even after the application process. So at this point the OP would have to lie or provide the transcript. (But I'm not buying the fact that this was never asked in any fashion during the application process).
Just discuss it with the school. I mean, it was bad to lie, but what is the worst they can do? reject you. If they reject you, just ride out your Irish med school, do well, and try to secure a US residency spot. We must lay in the bed that we make. There is no point in looking back. Good luck.