Well I would say that the time to do the mod is sooner rather than later. You'll be much happier with the tighter 180 scale. In the meantime, if you don't want to do the mod for some reason, you could use the procedure for doing the mod to open up the meter and adjust the potentiometer to allow the attainment of 550 with a quarter. There is an internal adjustment for this. Or you could send it back to Minelab and have them fix it. My vote is to do the mod.
Here's a link to a very detailed post on how it's done, including the internal adjustment of the potentiometer if you decide to just go that route.