Some ESCs want to see a neutral signal for a full second or longer before they will engage reverse. Try letting it sit there for a second in between the first and second push. I fit still does not work as it should, you might try to re-calibrate the endpoints and check again.

I am not sure if you have the brushed or brushless RTR version, but the SXX ESC will only run sensored type brushless motors. Even if you have the brushless RTR, it comes with a sensorless motor. I would recommend an ESC that will run the motor you have now, plus brushless when it is time to upgrade again. I suggest the Tekin RS.