To disorganize, mix together, or confuse someone or something. A noun or pronoun can be used between "jumble" and "up." I think you must have jumbled up the message because he and I agreed to meet on Thursday, not Friday. Be sure to jumble the entries up before you pull one out of the box.
jumble something up
to make a hodgepodge out of things. Who jumbled my papers up? Who jumbled up all my papers?
To mix some things up in a random, confused, or disorderly manner: The toddler jumbled up the puzzle pieces. The cat jumbled the yarn up.