folks need quick help

short story: dated girl, didnt work out, i suggested ending it 2/3 days ago, we agreed mutually to remain friends, she said she wanted to end it before but was glad i spoke out first. here is the problem: whilst dating her i was introduced to her best friend, who i only saw twice. that best friend invited me, her and two other friends for dinner which was supposed to be in a few hours.

for whatever reason her friend just sent a facebook conversation to all people invited and for whatever reason i was added, meaning the friend thinks i am coming, which i suppose means she doesnt know we are not seeing each other...i cant imagine that she would add me knowing that i just ended seein her friend.

its really akward as i have no intention of going there. so what do i do? say i cant make it for a bs reason or just ignore it. i would opt for ignoring it, but its somewhat unfriendly and might come across that i hold a grudge or am not over it??

suggestions!!!

Ignore it. She's in the past. You have no obligation to talk to her or any of her friends.