Both are OK in this context. The present tense sometimes can be used instead of the future tense. It is similar to what we say in English; "I am going tomorrow." (Yarın gidiyorum.). You can use "I will go tomorrow." (Yarın gideceğim.) instead here and both has the same meaning. So, "Yarın giderim/gidiyorum/gideceğim." are all fine. But when present or present continous tense is used in the future meaning, there is generally a time indicator word like "yarın, bu akşam, seneye".
Please tell me whether my explanation is correct: This can only mean "you sent" and not "he sent"? The ambiguity between the two only appears with the definite accusative ending (-InI), because the "n" for the second person and the "n" that is inserted for separation of the two i are not distinguishable? "He sent" would in this sentence be "Gönderdiği"? Here, the participe is an adjective and thus takes no case ending?