Let me quess: You’ve recorded your MIDI with “All MIDI inputs” selected for your track. If so, you may have accidentally recorded everything twice. “All MIDI inputs” should be used with care and only if you know, what you are doing.
Your keyboard is probably sending MIDI data on two different ports, i.e. USB A and USB B. Either tell your keyboard to only send it on one of the ports, select a specific port other than ALL MIDI inputs for the input to the VSTi, OR tell Cubase not to include one of them in “ALL MIDI inputs” (Like FunkyDrummer said).
HTH
J.L.