Do you by any chance have the "Developer Options" been enabled on your phone? I ask because that is what usually causes this. Messing around in there can be very bad for your phone, if you don't know aht you are doing.
If this is the case, I would really suggest not messing around in there, again, unless you know what you are doing. I say this because in most phones, the only way to turn the "Developer Options" back off, and keep yourself from doing any damage to the phone, would be a factory rest of the phone.
If the "Developer Options" are enabled on your phone, then that is where you need to go to turn off the reversed screen.
In "Developer Options" look for a check box that say "Force RTL layout direction" and turn it off. This should right your screen.