I've never used GoPro media, but on a side note, 'upload' means to transfer from a local computer to a remote computer over a network. Here the correct term is simply 'import'.
The "keep existing settings" prompt means that the settings for the sequence do not match the properties of the first clip you're adding to it. Premiere is basically asking if you want to change the sequence settings to match the footage. If you opt not to, then the mismatch will result in just the kind of "zoom" effect you cite.
I don't know what to tell you about the fact that the video is inverted and black & white.