Hi Doc!!
You only need to visit Kerah once! Forget about the portal you found near her, you'll never use it. All you needed were 1) the obelisk of light and to open the treasure chest in the small land area after swimming out from Kerah's area. When you opened that chest, the leprechaun should have appeared and said something about you having found his treasure. Take whatever you found (gosh, it has been so long I cannot even remember what the item is! whoa!) back to the pawnshop to get credit for that quest.
You're fine, you just don't know it!
Wyv