What I mean is I doubt the sentence attached. Should I use will or going to according the context from your view?
Please type sentences you wish us to consider into the body of a post. Are you aware that the image you have uploaded does not even list "am going to" as a choice. Assuming the context is normal, "am meeting" is the best choice.
"I think I am meeting him at entrance B. I can't remember." This means that, although the speaker can't really recall the plan, he or she believes that the plan was for him or her to meet the referent of "him" at the entrance labeled B.