"Oh no...I've really messed up... I sent the email about stupid Peter... to stupid Peter!!!"
Mess up – messed up – messed up
Meaning: If you mess up, you do something wrongly or badly, or you damage or spoil something.
Grammar: This phrasal verb may or may not have an object. If there is an object, it can go after the particle or between the verb and particle. If the object is a pronoun, it must go between the verb and particle.
She messed up
She messed up the plans
She messed them up
She messed up them - NOT CORRECT
Example sentence: Sarah messed up and took the wrong documents to the presentation.
Synonyms: make a mistake, screw up, get (something) wrong
From: BBC Learning English - http://www.bbc.co.uk/worldservice/learningenglish/