Sounds like you have a standard spring wastegate actuator, as that is very typical what you can adjust the boost to with a standard spring actuator.
Two options:
1. Cut about 1/8" tp 1/4" off of the adjustment rod, effectively making it shorter.
This is what I am going to do.
2. You could get an RJC boost controller and run more boost with a standard actuator.
Already have a RJC MBC