In spanish it's incorrect grammar said "Me atrasé, ¡ estoy tarde¡¡¡" I recomend you change it to one of this options: (all of them are informal spanish in mexico)
"Chin, Se me hizo tarde" (Chin = Oops; tanslate: Oops, i'm late)
"Voy tarde¡¡¡¡" (If Maccon it's talking to himself, this phrase it's better,)
"Perdón, ¡Perdon¡¡¡¡, se me fue el tiempo" (If Maccon it's talking to the teacher, Mexicans use to start an interaction with an excuse when we think we are doing wrong or when we are going to talk with an authority)
-------
Then again Maccon apology to the teacher... In Mexico we change our language to an informal way when we get scold, so it's better only said "Lo siento"
-----
The annoyed answer it's to long.. Our teachers use to said only "Primera advertencia, toma asiento"