A family of Microsoft word processing software products for creating web, email, and print documents.
Most likely the first page header paragraph mark or the Header style has space after in paragraph formatting (Format>Paragraph>Spacing>After).
You're also having issues because most rows are not breaking across the page boundary. This could be because the paragraph formatting of the table text is set to keep with next (Format>Paragraph>Line and Page Breaks). Or it could be that the row properties are set not to break (Table>Table Properties>Row>Allow row to break across pages).
You table does not appear to be inline with text, since it doesn't align with any of the margins. Check Table>Table Properties>Table and change Text Wrapping from Around to None.