First of all you probably will be fine, if there was an issue you would be aware of it.
If you are aware of any issue, you should declare it in writing to Revenue BEFORE the audit begins. This is very important, it can reduce or eliminate any penalties.
If you have been playing fast and loose, claiming expenses that you are not properly entitled to or what ever, how much is the tax on that likely to be, could it be a significant amount.
Unless you have undeclared income the amounts identified in any audit are likely to be small.
They will agree to a repayment schedule, 10 months is common. 2 to 3 years is not likely to be acceptable.