Was In The Lap Of The Gods(Not "...Revisited") only performed once?

Yeah, that's what I wanna know...only at The Rainbow?

No.
Check http://www.queenconcerts.com/live/queen/sha.html for more details.

It was most likely performed at every Sheer Heart Attack tour concert.  The song is on every concert recording from the era so far.

http://www.queenlive.ca/songs-queen.htm