If you're encountering ANY incidents of double-fires, there's significant issue(s) with the gun, probably with the critical fire control components, such as the sear.
I would contact Ruger, and see if they'll service it (I'm unsure of the level of support they're currently providing for the P85/P89 series guns). Ruger would be my first recommended source of problem resolution. Additionally, if they have not previously applied the Mk II safety modifications to the gun, they can do so then as well. If they'll service it, they'll give you some specific instructions on how to get it to them. They'll also likely go through the gun in its entirety, examining it and bringing it up to snuff (factory specs) as needed.
To recap: Until resolved by a competent authority, your P85 is unsafe to use. Once fixed, you'll love it-but don't use it until the problem(s) is/are resolved.