On Friday of the last week, I couldn't really think that there was my class with you. I mean that i was concentrated somethin relate to my graduation while my phone was ringing from you. I'm so sorry.... I would like to call you again. But Unfortunately, My phone battery was dead.... See you later :-)

On Friday of the last week, I couldn't really think that there was my class with you.
   =>  On Friday last week, I didn’t remember that I had a class with you.

I mean that i was concentrated somethin relate to my graduation while my phone was ringing from you.
   =>  I mean, I was preoccupied with something related to my graduation when you called.

I'm so sorry....
   =>  I’m so sorry.

I would like to call you again.
   => I really wanted you to call me again.

But Unfortunately, My phone battery was dead....
   =>Unfortunately, my phone’s battery drained.