There was a period of time when my daughter was sounding out words correctly but then blending them incorrectly, and I was astounded by how much patience it required from me (For example, she'd say st-i-ll, but after blending it would come out "skrivel"). And then all of a sudden one day, it just CLICKED. It was a beautiful moment. Either keep at it or take a break for a month or so and focus on simpler, 3 letter words.