I'm updating this in case anyone runs into this issue.
Site admin > Grades > General settings > Grade point maximum.
The other setting to check is Site admin > Grades > General settings > Unlimited grades to allow point values that are over 100% for a given item.
Make sure the Admin setting "Grade point maximum" / gradepointmax is >= the largest assignment at your school. It defaults to 100.
Also if you create a grade item through import it defaults to 100, so creating it first with a point total of 150 and /or allowing "Unlimited grades" / unlimitedgrades. Though you will still need to change the max grade to 150.
Barbara