Currently the number of teeth on the X-axis motor pulley engaged with the belt is too small - it will slip. You should put an idler either side of the motor pulley to force the belt to wrap around it.

The travel on the Y-axis is limited by when the Z-axis makes contact with the X bearing block support, so there is a gap between the position of the Y bearing blocks at this limit and the gantry sides. Therefore you could space the Y-bearing blocks out further (with longer rails to match) to add strength without compromising travel.

The piece of aluminium extrusion underneath the gantry that links the two sides doesn't really add any strength since the gantry is well supported there by the ballnuts. I would get rid of that extrusion and clearly shorten the gantry sides where it was. The Z-motor mount can also be made narrower near the motor to save material.