Can I get charged with a DUI if I wasn't in my vehicle and the officer didn't even see me driving?

I was arrested for DUI. It started with an argument between my fiance and I. She lives 30 miles away in another town. It was Sunday night, and after drinking a few beers ealier in the day, decided to go see her and work it out. I was knocking on the door, when her friend , who lives a couple of houses down , came up behind me and said the cops have been called by her. There was no domestic, no malice, I didnt even say a word to her. I returned home, and was in my driveway, getting out of the pickup, keys in my pocket, ready to go in the house, when a sheriff pulled up and began to question me. I had beer in the pickup which he noticed, and arrested me for DUI. I performed the roadside, and did not feel I shouldnt have been driving. I took the blood test. My fiance have worked things out and are fine. She and her friend feel terrible the cops were even called. My question is this a legal seizure? The officer didnt ask for truck registration, proof of insurance , nothing to prove it was even my truck. Im not even sure the officer seen me driving. I was five steps from going in the house when he pulled up. Can you help me with any advise, other than hiring an attorney.? I strongly believe my blood will be under legal limits, but do not have the results yet. How long does the blood keep?