OP wrote, "I agreed to go to the Sunday morning session."
So, you should honor your word and go to the convention in the morning. Take separate transportation. When it ends, say, "Thanks for inviting me It shows you care for me. I heard nothing new that I haven't heard before.(Or, if it is new, like New Light's Overlapping Generation Change . . . then discuss that briefly. 'I was stunned to see the New Light. It seems the Generation Teaching has changed alot, again. I don't think the Society knows what it is doing on that one."') I have plans for the afternoon. I'm going to (x). Would you like to join me?"
Next time they ask you to attend a meeting (which will be coming), then you are going to have to deal with it.