What should I get?!

It maybe sounds so childish but, I want to cry...

I know I should be mature already regarding this matter, but i can't stop myself for wanting to cry...

The day after tomorrow will be my little sister 15th birthday and till today I haven't have any gift yet! Oh God... my father promised me that he would take me to Anime Shop that we usually go to buy a gift for her (which I can't go there by myself because it kinda far).  I even already canceled several of my appointments just for that! But up until today, I just sitting at home with empty hands, no gifts.

I know that my father is busy with his work and so does my mother (that's why i didn't ask my mom in the first place).  But he said that he can and today... Before (two days ago to be more precise), he promised me that yesterday he will take me to there, but then, he said he had a work to do.  "Okay, maybe tomorrow..." I thought. He said that today he will take me at least not to the Anime Shop but to other place that maybe I will find my gift. And then, when I came home from school today (that I was put effort in to came home faster than usual), I found out that he already left to work (he got a call and then left in rush according to my mom).

I know I should understand that my parents hard work is for us,  their children after all. But still, i feel disappointed. I know I'm not supposed to mad but I just... disappointed.  I feel like I was betrayed. Oh God... my tears fell...

Now, I really don't know what I'm supposed to get for my beloved sister... (Yes, i kinda have a low stage of sister complex.  Don't blame me. I love my family after all...)