First make sure the xl-5 is not in training mode (50% power).
If not the case, take them one by one
If motor has mechanical timing (by rotating the endbell), for now just set it to 0. Later on you can play with it.
On the remote, set throttle channel to default (normal not reversed, middle at 50%, endpoints at 100%, no trim/subtrim, no expo)
Calibrate the esc. Pay attention to calibration sequence, not to confuse by accident throttle and reverse.
Only at this point, if the car runs backward, swap motor wires.