Am I wrong for considering not going?

So my sister called me saying she needs to borrow my car for something she is doing for the girls at her school. She doesn’t think her car will make it. I had plans this weekend though. I planned them weeks ahead. And I also have to come back up here. It’s a 40 minute drive each way so either way if I come home I won’t be able to go back. Now my grandma’s making me feel bad because I don’t want to go home and cancel my plans. I don't know what to do.
Am I wrong for considering not going?
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