What is Gatsby's concern about Daisy and the party? Is it valid?

The following Saturday, Tom and Daisy attend one of Gatsby's parties. Tom, predictably, is unpleasant and rude throughout the evening. After the Buchanans leave, Gatsby is crestfallen at the thought that Daisy did not have a good time; he does not yet know that Tom badly upset her by telling her that Gatsby made his fortune in bootlegging. Gatsby is really obsessed with an idea of Daisy rather that the person she is. Consequently, all his interpretations of her are not based on reality.