Unfortunately - as long as you did not file the sales tax return - there is no any statute of limitation and you are still liable for the sale tax.
Please verify if you paid sales tax on any supply - that will reduce your sales tax liability.
As that was a honest mistake - I suggest to apply for forgiveness of penalties.
You might need a local CPA or Enrolled agent to represent you with KY DOR.
Let me know if you need any help.