Move the gantry towards the back of the Y-axis. You will have to apply a bit more force than earlier to move it since the ballscrew is now connected to it.
Fully tighten the 8 screws and locknuts, of both the motor and the bearing support.
Move the gantry towards the front of the Y-axis.
Fully tighten the 4 screws and locknuts of the bearing support.
Animation
Take time to make sure that the ballscrew assembly is correctly aligned, since this will improve the overall performance of your machine.