Do you have any temporary boost potions? If you're getting close to taking out the level 18 abomination, a small boost to one or more stats may be enough to finish it off quickly enough.
Have you summoned your creature for support, or at least a distraction?
Have you finished off everything else on the island?
You can return to Broken Valley and then take the path to the far south west into the fjords; I did that after Maxos temple, before going to Sentinel Island. The first couple opponents got me to level 16, clearing down the mountain path brought me to 17, and swimming over to another couple beaches almost brought me to level 18. I had to take out a few level 21 imps to get to level 18, which was much easier after I switched my creature from a warrior head to a ranger head (and once I found a mage head I switched to that).
You need to get the ring from Laiken's Study in order to continue the main plot quests and get the dragon stone (after taking over the battle tower). You'll want to finish off pretty much everything in Broken Valley and on Sentinel Island before doing that, though (there is a warning at the 'point of no return'), as most locations and NPCs will no longer be accessible. You can wait to rescue the miners in the quarry tower in Broken Valley, and must wait to get the book from the boat in a tree on Sentinel Island (though you may want to read the book yourself, rather than complete the quest).
Welcome to the forum.
