After leaving the Stygian Johnson Gang house, Carter snuck into the hospital to buy something to clean his wounds. He then went to the toilet in the mall to disinfect and clean the wounds on his shoulder and leg.
A gunshot wound was not an ordinary wound. This kind of pain was very bothersome even though Carter could stand it.
Worried that the people from St. Piaf would find him, he hid in the toilet carefully the whole time. After that, he only left the mall when it was time to meet Shirley.