What evidence in The Great Gatsby suggests that Gatsby is wrong when he insists you can repeat the past?

This section of the novel comes at the end of Chapter Six,
after Tom and Daisy Buchanan have been to one of Gatbsy's parties for the first time and
Gatsby is convinced that Daisy did not enjoy it. Gatbsy, "incredulously," asserts his
belief that you can repeat the past, and Nick goes on to
comment:

He
talked a lot about the past, and I gathered that he wanted to recover something, some
idea of himself perhaps, that had gone into loving Daisy. His life had been confused and
disordered since then, but if he could once return to a certain starting place and go
over it all slowly, he could find out what that thing
was...

Thus Gatsby's desire
to "repeat" the past is his attempt to return to his halcyon days with Daisy, before she
married Tom, where everything was wonderful and perfect. However, the fact of Daisy and
Tom's daughter intrudes as an unpleasant reminder that it is impossible to return to the
past. Note how Nick describes Gatsby when he sees
her:

Afterward
he kept looking at the child with surprise. I don't think he had ever really believed in
its existence before.

Their
child is a tangible reminder that Tom and Daisy did get married and that it is
impossible to return to the past now.