Hello @Florida Bear and welcome to SGL.
A 13mm eyepiece gives x50 - thats the focal length of the telescope divided by the focal length of the eyepiece, so 650/13 = 50.
At the moment Saturn is well past closest approach so is very small.
You can certainly use shorter focal length eyepieces in your scope, for the planets I would suggest x185 (a 3.5mm eyepiece) is good.
Or you could buy a x2 barlow lens that doubles the focal length of your telescope to 1300mm and then use a 7mm eyepiece to get x185.
Comets are dull smudges even in bigger scopes.
โstellariumโ is a great piece of free astronomy software that you can download to see what is in the night sky.
Hope that helps.