Very few toner-based printers can truly print edge to edge. That's why when you print on an 8.5"x11" sheet, even if you print to the edge, you will likely find up to 0.25" white margin around the page. There is nothing you can directly do about it.
That is exactly why FedEx Office recommended printing on 11"x17" which would have allowed for the full 9"x11.5" printing area, including bleed, to be printed on the sheet and allowing you to trim it to 8.5"x11" with printing to the edge via the bleed per your design.
- Dov