OK this looks like the surface of your bed isn't flat to the same plane as the gantry which is quite usual with these cheaper routers, even my Teckno Isel router varies over the bed.

Trick is to get a sacrificial plate and get the router to mill this flat, don't move it and attach to that.
You can buy some gel mats that are sticky on both sides to hold flat panels securely without bowing, not cheap but they do a good job.