well do you tell them you are eating and ask if they have plans before making food? how old are you?

If they make plans without telling you, they can go without you. Don't let them push their shit on you.

So you're involved with the family enough, or young enough, that they dictate your schedule. Yet you cooked an entire meal only for yourself, not as a family or shared meal. I think the communication issues go both ways here.

happens to me too sometimes. I just tell them to leave without me.

Tell them "Have fun and/or good luck" and continue on with your meal.