Ethics_101

Okay, here's the deal: I was recently admitted into my dream program with 5-years of guaranteed funding. However during the application and interview process I knowingly withheld information about two previous [failed] attempts at doctoral studies. While I have justification for withdrawing from both of these programs, I chose to withhold this information because I knew it would hurt my chances of being considered and/or admitted. At the end of the day, what graduate program would want to admit a student who withdrew from PhD studies not once but twice?!? I know this was a highly unethical decision on my part and for this reason, I feel that I should simply decline their offer of admission to avoid any embarassment in the future. [Note: This is the ONLY program I applied to this year]. However since this is my DREAM program, part of me wants to say and do nothing, and hope the Graduate School doesn't find out. After all, don't admission offices track students through the National Student Clearinghouse and know where I've enrolled in the past before making an offer of admission? Wouldn't they see that I didn't declare univeresity X & Y on my application? Yet another part of me feels like I should send an open letter to my POI, the department's admissions committee, and/or the Graduate School and explain the poor decision I made in the application & interview process. At least they'd have all the information I should have provided from the start, and can make an informed choice on whether to accept me or not. Any thoughts or advice what I should do?