Can I use a bonding terminal on ground wire between ufer rod and panel
There's an easier fix for this

Get a Siemens EC1GB82 ground bar kit and mount it to the bottom-most set of ground bar holes in your loadcenter cabinet, with the large lug down.  Then, you can simply terminate the annoyingly short ground wire to the bottom bar's large lug and call it a day.

This works because all the ground bars on a panel are electrically equivalent -- the cabinet connects them all together, by virtue of itself needing to be grounded.