If you really are struggling, you could go to the opposite side of the world and look for a spawner there. Usually, though not guaranteed, each boss spawner is generated in each quadrant. Like i said it's not guaranteed but it is common, so you may have to find a different spawner, simply explore away in the opposite direction, which may be a bit annoying, but it's that or creating a new world, or adapting to the plains enemies by a strategy or skill.

Deathsquitoes which are notorious for causing issues for newer players are glass cannons, if you have a bow, try to snipe them out, or, let them come close enough to attack, and dodge roll it, after that it'll circle you until it starts to fly towards another attack at which you've got an easy shot. Fulings deal a ton of damage, though their AI seems to be similar to greydwarfs, to deal with those, you can use a bow or an atgeir as it's range and ability to stagger enemies is tremendously useful.

Other than that, best of luck.