I'm inserting your screenshot below so that people others don't have to download the PNG to see your example.
I see the that source sequece is 568x320, as well as your output settings. Is 568x320 the size of your source footage? Honestly, by today's standards, 568x320 is pretty low quality to begin with.
As far as the sequence goes, even if you have super high-quality images, if you're only exporting to 568x320 size, the entire video is going to look pretty small (or low-quality) on most modern screens that typically have sizes of HD (1920x1080) or 4K (3840x2160). Just doing a little math, 568x320 isn't even half of HD.
As a "fix," you could create a sequece closer to HD or SD and bring everything into that. If your source footage is only 568x320, then that's not going to look as good (and you'll have to upscale it). But everything else, assuming that it's all higher quality, will look better.