Your background WAS clean until now. The best thing

you can do now is tell the truth and really show your remorse. In US, remorse is very important to get sympathy from police or judge. If you keep lying(which police can easily tell, they deal with all kinds of people everyday, trust me), they will believe you have absolutely no remorse which means you are most likely doing the same thing again. That's no good to you. The more remorse you show, they will believe you the less likely to do the same thing.
You are smart guy, if you were a cop, will you be so stupidly cheated by another person? Will you give a chance to the person keeping lying to you and showed no remorse?
Go figure!