How much interest am I able to charge on a construction contract that the debtor is 11 months late to pay on.In my contract I write 3% added a month 24% annual. Is this within Marylands laws?

Contract signed by property owner agreed to amount. Property owner paid half amount after job was completed. My contract specifies the conditions listed in above question. Am I able to include those additional fees or is there any Maryland law that entitles me to collect more additional fees than what are outlined in my contract? I am a residential contractor