EDIT Look at the "square" relay terminal, the one pretty much in the middle of the relay THERE SHOULD ONLY BE one wire going to that......and it should go from there directly down to the starter solenoid. (small terminal) Did someone install a start "push button" in the car?
EDIT....SECOND thing to try is disconnect first one, then the other, of the small "push on" wires off that relay. If that does not stop it, disconnect the wire going to the "square" terminal. If THAT does not stop it, time to get down to the starter. You may have inadvertently jumpered the two starter terminals across, IE either swiveled one of the wires when tightening, or they are otherwise touching. If not that, then a solenoid problem.