Step #3 is not required to install this Addon, and is only recommended to BACK-UP here admin.php?target=database before moving forward, it is highly recommended. What errors are you seeing, all you need to do is PASTE:
INSERT INTO cscart_settings VALUES (20199, 'xml_sitemap', 'Addons', '', 'C', 'Y', 600, 'Y');
INSERT INTO cscart_settings VALUES (20200, 'include_products', 'Addons', 'xml_sitemap_opts', 'C', 'Y', 1, 'Y');
INSERT INTO cscart_settings VALUES (20201, 'include_categories', 'Addons', 'xml_sitemap_opts', 'C', 'Y', 2, 'Y');
INSERT INTO cscart_settings VALUES (20202, 'include_manufacturers', 'Addons', 'xml_sitemap_opts', 'C', 'Y', 3, 'Y');
INSERT INTO cscart_settings VALUES (20203, 'include_pages', 'Addons', 'xml_sitemap_opts', 'C', 'Y', 4, 'Y');
INSERT INTO cscart_settings_descriptions VALUES (20199, 'XML Sitemap', 'O', 'EN', '');
INSERT INTO cscart_settings_descriptions VALUES (0, 'XML Sitemap', 'U', 'EN', 'xml_sitemap_opts');
INSERT INTO cscart_settings_descriptions VALUES (20200, 'Include Products', 'O', 'EN', '');
INSERT INTO cscart_settings_descriptions VALUES (20201, 'Include Categories', 'O', 'EN', '');
INSERT INTO cscart_settings_descriptions VALUES (20202, 'Include Manufacturers', 'O', 'EN', '');
INSERT INTO cscart_settings_descriptions VALUES (20203, 'Include Pages', 'O', 'EN', '');
INSERT INTO cscart_settings_subsections VALUES ('xml_sitemap_opts', 'Addons', 600);
into “Update Database” text field here admin.php?target=upgrade_center