What should i do in the situation?!?):?

im 13 years old(: so today i was rlly busy and apparently my friend called while i was gone. i didnt notice that i had a missed call until 11pm tonight... and she left a message asking if i cud hangout tomorrow... but i didnt want to call bac because it was 11pm and also tomorrow ill be leaving for vacation for 2 weeks. but now i feel guilty for not calling back, and that she might get mad and feel as if im ignoring her.. for not calling bac for 2 weeks because i never mentioned that i was going on vaca.. shud i just wait until i get bac from my vaca to call her? or wat wud u do in this situation?