Yamaha P35 Midi input registering all wrong/multiple notes

Hi guys,

I am going out of my mind here. I have a Yamaha P35 plugged into my Macbook air via a Midi-to-USB cable. The Mac and Garage Band detect the MIDI input, and I get a notification. When I play, GB detects it,, but all the notes are wrong. For example a simple C chord could trigger 6 or 7 notes to play simultaneously, usually a few octaves lower. Everything is a jumble, with no rhyme or reason. Sometimes though, I can hear what I played properly so it's definitely registering but something is going wrong somewhere and I have no idea how to fix it.

I've installed what I believe is the latest driver. I have no idea what to do. I just want to record a simple piano piece.

Please help!