Going thru customs after overstaying visa in Dub (Dublin)

I am American. I have overstayed my 90 day tourist visa by 8 weeks. I am returning to the states in a week. I am very nervous about going through customs in Dublin. My plan was to tell them I had been in Belfast for the last couple months (knowing in N Ireland they do not stamp your passport and technically get 90 more days in the UK) I do not know if this will work because I do not actually know anyone in Belfast to vouch for me, nor do I have any valid proof I was up there. Am I over thinking it? Maybe they could care less, but it appears as if I have broken the law and I am fearful of getting banned for 5 years. Has anyone been through this or know someone who has? Advice, knowledge, help please... THANKS!