every enemy, including bosses, will chase you until they lose you (enter a instance or get far enough to hide long enough to shake them, get out of LOS). Most rubberband back to near where they were pathing, but some will hang around for whatever reason. The critters are not hard leashed, though, and they only go back home after totally unable to find you for a while.

Shoot him and use the stones to hide behind when he shoots and runs at you

Make sure you are well fed, 3 foods. at that level cooked meat/grilled neck tail, berries, mushrooms, honey are your options. Honey has the best health regen by far so good for boss fights.
Make sure you have your resting buff at all times as it increases xp gain, health and stamina regen. If you need to refresh it on the go just build a campfire and sit next to it (x) for 30 seconds to get the 8 min base buff back. Always start a boss fight in the morning, fighting at night is a mistake due to the cold debuff and more enemies around.
Remember there is no rush and its easy enough to avoid the first bosses attacks if you need to regen health or stamina, just keep a big rock or two between you and him.
Either a bow or a melee weapon will do, he's just the training wheels boss fight.
Valheim is very much a game that rewards careful preparation and punishes rushing into things, so take your time to gear up and all and things are a cakewalk.

If you hold right mouse and hit spacebar you will dodge roll. Dodging his attacks makes it really easy. Best foods for most stamina, rest and daytime. You can even put up a fence around his spawn and shoot him from inside his stone circle... dodging around the stones is faster though... less prep time.

Thanks guys, excellent advice. I should be able to handle it now!

You could lure him out, far away from spawn. If you initiate fight and don't finish a boss, it's hp will return to 100% but aside from that and if away - he will wait for u.

if that's some nasty bug with that boss doing you instant before you get any chance to run few meters so u can try to escape, drop me an invite, I'm online for an hour or 2 more and can simply help u with that fight

Thanks for the information. It's not bugged, I was just surprised to find that the boss would follow you and stay wherever you die most recently.
Since there are no character levels, and I died so many times I have no skills built up, I might as well just start over this time.

The wood shield will block his attacks, both the lightning and the antlers. Keep the shield up until he uses antlers, then you can get a couple hits in before he runs around.

But yeah, bosses don't despawn if you don't kill them, and it's also possible to summon more than one at the same time, so don't spam the offerings.