Hi,
all 500 canopies fit all 500s (same for 600s but the 690). With the canopy holders, at least, they are different, but you could also adjust the existing ones.
Where does it not fit? Maybe you didn't notice that the 550 has a longer stance, front skid bow to the front skid mount, like on the 600?
If it's only tight, you can always sand the front recesses a bit, where they fit the front skid bow. Do a couple of iterations, always taking away only so much, so it doesn't become a loose fit.
Kind regards
Eddi
Born to fly ...
forced to work.