Did I make a big mistake?

I purchased a 2003 Rancher 350 es. I purchased it without a pink slip as I planned on using it for work around my property and nothing more. The seller said the quad was his father’s and his father was terminally ill. Which made sense the quad is very sun faded and has 260 miles on it. So I went to look at the quad and met with the son and his grandfather. I explained to both of them that I had no interest in buying a stolen quad. They offered to go to the police dept. with me so I could have the vin. number checked and be assured the quad was stolen. We went and the officer ran the vin # and said the quad was not stolen.

Now I’ve been riding for a few days and it’s so much fun I think I will want to trail ride. My next green sticker is due in June of 2016. I called the seller and he said if I took the old registration card into the DMV next May I can pay for the green sticker and the quad will remain in his fathers name.

Can I do this or will i have to keep the quad for work around my property?
thanks
Neal