So the bottom of my print is not solid, how do i solve this?

[sugarfreemilk 0]

[Slashee_the_Cow 480]

If that's the bottom of the print facing the camera, that is solid, it's just being printed as walls (red outer/green inner) rather than skin (yellow) because walls take precedence over skin if there's not enough room for both.

 

If your wall thickness isn't enough for three walls, then it's probably being controlled by Top/Bottom > Small Top/Bottom Width which defines a minimum width for a section to be printed as walls rather than skin to prevent a lot of small, jerky motions in narrow sections.