Oh honey you're not doing anything wrong! I felt like every time I got the hang of where my kids were & what they were doing, they would change! It's gotten better as Pie has gotten older but in the first 12 months it felt like she was changing her pattern every couple of weeks. I do think she dropped her third sleep around this age, so it could be that.
I second what Marcellus said - go with what works & don't overthink it (it will all change again soon anyway! )