How Should I Handle This?

I live 4 hours from my family. So they don't get to see my children as often.

My mother will typically ask to keep them for a weekend...No problem. We'll meet half way and that has worked for the both of us.

Lately, (the last 3 times) when she asks for my children and says she wants them for an extended period of time I look over my calendar and make sure we don't have appointments or visits with their dad coming up. He is usually absent but in the off chance he follows through with plans he's made to see them, I like to keep the girls available for him.

Anyway...... She'll ask for them for an extended period of time such as 2 weeks or a Thursday - Sunday or etc. I always ask is she sure and she says yes. So then, I make plans for that weekend or those days when I don't have them. Some plans include me paying in advance for maybe a hotel room or event. Idk why, but she'll tell me at the last minute, hey I decided not to keep the kids for the time frame I said and you'll need to come to me to pick them up. And it's usually so last minute that I leave work early that day or a couple days later drive and pick them up. I don't ever complain, I just hop up and go get my kids. In a way it's starting to make me feel like they're unwanted there. It wasn't like this before.

Granted, I know that my children are my responsibility. I'm not complaining but it is frustrating when this happens. I don't get a lot of free time just for me so I try my best to get in self care or night away from home when I don't have them.

I've tried talking to my mom and explaining that if she doesn't intend to keep them for the time frame mentioned, it's only fair to actually tell me that ahead of time because I don't just sit around the house. I try to get out and breathe a little while the kids are away but if she keeps changing her mind on me last minute then I'm going to stop letting them visit unless we happen to make a trip there all together.

I know my title reads how should I handle this but the most appropriate question is.... Was I wrong? Should I have handled it that way?

And don't come for me saying I sound entitled or anything of the sort. Picture it as someone canceling plans on you.

Edit: Thank you so much ladies!! 💓. I hadn't ever thought of the things y'all are mentioning. Because she asks for them, I was letting her lead the way assuming she had a handle on it. I really appreciate it y'all 🙏