I like what everyone had to say in their responses. I'd like to add that you don't really owe anyone any explanation or justification for your boundaries. If you don't like last minute cancellations, you have every right to plan your life without having to consider those people.

In my experience, because I got tired of waiting for people to commit to plans, I decided to just do what I wanted, tell people what I was doing and where I would be and if they cared to join, great! This led to one of the greatest years ever, with people truly interested in hanging out.

The people who don't like your boundaries, are usually the ones to believe you're somehow being unpleasant or disagreeable. That's okay!

Hugs.