Take the written agreement to a real estate attorney for review. No one on the Internet is going to be able to guide you without reading the agreement and looking into what has occurred between you signing and moving in and now. Too many variables.
I agree with Mr. Beuhler. The contract is going to carry the day on this, and without seeing the contract it's impossible for anyone to give sound advice.
I will say that if you are purchasing the home in a seller finance situation, you do have an equitable interest in the property. With that, I can't imagine the seller can simply "evict" you with a 3 days notice as this is not a rental, and secondly there are proper eviction procedures the owner must follow even if it were a rental. Take the contract to a real estate/contracts attorney near you and have them look it over. My suspicion is they will tell you she can't kick you out unless there has been some serious nonperformance on your end..
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The terms of your contract will control. I've seen lots of different ways that people do this kind of arrangement; most of them have some kind of problem, and sometimes those problems will benefit the buyer/tenant.