And since someone in this thread brought it up, is there something wrong with telling Auntie that we'd need a day or two to think about it because we weren't sure what we were doing this weekend? It is Father's day this weekend, maybe we already had plans or were considering making plans. Is there something wrong with making sure my schedule is 100% clear before accepting?
I think people were thinking that you were waiting to see if another better offer came up before you made your decision. Personally, I don't have any problem waiting to see what will happen, as several of my friends have work schedules that change with alarming frequency. Boyfriend could be fine, then as of Thursday evening he'll have to work all weekend, meaning any plans we had would have to be canceled. I don't see any problem with saying that you'll check your schedule and get back to her.
This is what it seemed like to me, because of this line in your post:
I told her we'd need a day or two to think about it because we weren't sure what we were doing this weekend.
To me, that says you need a day or two to decide what you are doing that weekend. Not to see if your schedule is clear, but to decide there is nothing better going on and you won't be missing anything by playing dominos.