Amdusias is level 15, so it would be better if you were, as well (giving you access to the Healing spell, Explosive Arrows, etc). Playing a ranger in DKS I found close range splitting arrows quite effective against bosses, though didn't learn it until later (character level 24). Some of the skills were modified a bit from the original release, and unique bows added, etc.
If you run at a bit of an angle and jump on your way towards Amdusias, you may be able to avoid his first Explosive Arrow, and get within melee range before he can use it again. Alternately, you could learn Rush Attack if you have a spare skill point (you will eventually be able to redistribute your skill points, for a price, so it will not be 'wasted').
You can reload a save before entering Amdusias' chamber, use the teleporter shrine in the centre of the hallways to leave the temple and then either finish off stuff around Broken Valley, or head to the fjords (mountain path in the far south west of Broken Valley).
When you finish off Amdusias you will get access to Sentinel Island. Your first encounter there you can mindread to go up a level, so the higher level you are the more of an experience bonus that will be (I made it to 18 in the fjords in the original release of D2:ED, and to level 22 in DKS). You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus (equip anything you have with a Wisdom boost).
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