Gods Of Merlin by Priya Ardis

Eowlyn Patience is a girl with NO future until she’s asked to kill her physics teacher.
Percy Jackson meets King Arthur when Someone must claim Excalibur.
She is so not the right person… Trouble follows seventeen-year-old Eowlyn Patience around. Desperate for her current foster family to like her, her life all falls apart when the actual Sword in the Stone drops like a dead bird into the heart of London. And suddenly she has to attend some weirdo school in England with the irritating smart kid from science class.
After a teenage Merlin wakes from a fifteen-hundred-year nap, he takes the name Matt Emrys. Now he must track down the next Arthur before the apocalypse begins. But the Avalon Academy trials are being sabotaged by vicious gargoyles, and his growing feelings for exactly the wrong girl are getting in the way.