When you create an invoice, it only captures the unbilled time/expense entries at that time. Any additional time/expense entries created after that invoice will not automatically be included, even if the invoice is in Pre-Bill state (i.e. not finalized).
You can either delete the invoice, but don't worry, the entries will not be deleted. They will go back to unbilled activity so another invoice can be created. Another option is to refresh an invoice and to follow these steps click here.
If you make a new invoice or refresh the invoice, the new time/expense entries will pull in automatically as long as they are dated within the date range of the invoice.