Sediment drain plug next to fuel filter rear wheel arch

Hi just serviced my 2004 Freelander TD4, and change fuel filter under the wheel arch, all went ok. I also removed the Sediment plastic plug and some water did come out. Did it back up and all sealed up. Great job done.
However, on floor near where I was working 1 rubber seal. I do not have leak from sediment plug but not sure if this had come off the plug when removed? should there be a seal on the plug on bottom of sediment.