Homeschooling

I could use some guidance on structuring homeschool. I'm on my second year of homeschooling. When the year begins I have a rough schedule all planned (with free and open time included). With time however, other things start slipping into our schedule making it hard to have a predictable daily schedule. Sometimes my non-homeschooling friends want to get our kids together during the day, or someone needs help watching one of their kids, or someone has a dentist appointment, or the daily tasks that need to be done take priority. I love structure, but have to be careful because I also easily lean toward rigidity. How can I be flexible with life while having consistent homeschool structure?