You're going for the meet up way too fast. With online texting you need to build rapport with girl and this will increase the chances of her being down to hang. You build rapport by having some logical normal conversation. Once you've built rapport go for a soft close once or twice e.g do you like wine? You should watch Alex's video on how to close btw. when she agrees to the general idea of meeting up then you can ask what her schedule is like.

The problem was you made her idea of meeting at the weekend, and suddenly she realized that was the same night. You could have said, "looking spontanious tonight?"