Added an extra zero?! That's an interesting one!
Anyway your exposure, assuming it was a Med1 of the 2006 tax year, will be interest of 0.0273% per day on the amount of under-claimed tax.
Make a 10% disclosing payment and Revenue will look favorably upon you. Arrange for to deduct the liability due from your tax credits. If you are unaware of how to go about this ask the auditor and he/she will explain it.
It's not going to be massive money.... Around €840 plus the interest.
Just don't do it again, what a stupid thing to do! Now be on your way!