What must be my reply ? Read my details below and answer please.?

I have a crush on a guy.I met him in a party and added him on facebook.He dosent respond to my fb msgs. Bt I sent his a msg yesterday to preside over a function in my college(He is a dancer). FOr that msg alone,he replied. But sadly, he replied this "Sis, sorry I cant come.Have work" :( He called me sister :( .So suggest me what shall I reply ? A catchy reply fr which he should reply back and keep thinking of me even after he logs out of fb... Pls suggest. No funny answers. No abusive tone. Please help !