If you are using the Xcode 7 GM build version 7A218, the chances are that you accidentally downloaded iOS 9.1 (13B5110e) as opposed to the iOS 9 GM build (13A340). I did the same thing don't worry. They are too close to each other on the downloads page :0
You can check which version you have on your device by simply going to your device Settings > General > About > Version
All you have to do is download the correct iOS 9 GM build and go to iTunes. Click on your device. In the summary tab, OPTION + Right Click "Check for Update" and restore your device by navigating to the iOS 9 GM build finder location. Note by selecting "Check for Update" you will not lose any settings or data on your device. In other words, it is not a restore
However, if you are using Xcode 7.1 build version (7B60) iOS 9.1 is supported
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