"My uncle has passed away recently, so I need to go to my hometown. Because of this, I won't be able to come to your reception. I'm very sorry, but I hope to see you another day soon. I hope you understand." Even though your original text was understandable, some of the phrases and words were too businesslike - it made your message sound mechanical and also made you sound rather cold-hearted. I've rewritten the text in an appropriately formal-yet-sympathetic manner. I can explain some phrases or choices of words, if you wish.

Suddenly my uncle has passed away. So I am going to my native country. Due to this reason I am unable to attend your reception. Sorry. I will meet you some other day. Don't take mistake. I'm not completely sure what you mean by "Don't take mistake." Do you not want the other person to be offended? Also, when someone dies, a nice way to say it is to say that they have "passed away."