If you have defeated Sin, and have access to the Inside Sin dungeon area, I think you should have access to all the temples. The Item that you get from the temple at Macalania is a Luck Sphere.
Check to see if you have access to the other temples. If you do I don't know what is wrong at Macalania. Check to see if you can get into Djose or something.
I assume you are sure that Macalania is the temple you missed, but I thought I should check that you did go back to Zanarkand to get the destruction sphere there.
Does Cid say "The final showdown with sin, let's get this show on the road" when you talk to him on the Airship. This is a good indication of whether you are at the very end of the game or not.
SPOILERS: (for anyone who hasn't finished the game)
You can go back after defeating Seymour inside Sin, but if you enter the tower in the next area, to fight Jecht, you cannot go back.
I thought I should let you know that this board isn't exactly active these days, and to my knowledge there isn't anyone that is "online". I usualy stop by at least once a day to answer FFX questions, but do not stick around. If you are looking for immediate answers to your questions you are probably not going to find them here. If you are patient I should be able to answer them. I may break out one of my old saves and try to figure out what is going on here.
I wish you the best of luck on figuring this out.
