Not only do you need to make it bigger on two sides, bu you need to figure out how big you want the picture compared to the borders. If you can get the 64x64" pattern (or even the original size, plue borders, so that the design in the middle won't hang over the sides), that would probably best for a queen bed, as the mattress size is 60x80. Then you need to figure out how big you want it (86x93 you said?) and what borders and how many you need to add to turn it into what you want.
I would make the mattress size be the middle (with added squares on top and bottom), then add borders to make it big enough to be slept under.
Sorry, I know some of the is jumbled, I was jumping around in my post trying to clarify, and I think I made it worse!
Anyway, good luck!