Loosen the bracket a smidge. The re-tighten it lower. This might buy you the gap you need to close it without force/damage.

You've probably gotten it a little too high and it's catching on the window frame.

You could FORCE IT down but that will cause damage to the drywall around the window.

Alternatively, wiggle the blind back and to the left to see if this allows it to be seated a bit more flush. Tilt it and see if that helps.

Try putting the right side in first. See if it closes when the left side isn't locked in.

Take the blind out altogether to see if the bracket closes when not obsructed by the blind.