Try turning the plastic piece over. Maybe the hole is just off centre. Otherwise hit the plastic bit with a sander. Looks like all you need is ~ 1/32" to 1/16".
There are usually more places than one to adjust. ... like where the rail bolts to the top. Are there elongated holes?
There are usually more places than one to adjust. ... like where the rail bolts to the top. Are there elongated holes?