I think you may be a.) extruding a bit hot and b.) under extruding
Try to fiddle with flow rate percentage a bit, and more importantly, when feeling brave, look into this extrude calibration is a must thread
Extruder Calibration a must - Snapmaker 2.0 - Snapmaker: where creation happens
The machine under extrudes quite a bit out of the box.
Under-Extrusion (simplify3d.com)
Consider looking into Cura for slicing, its more challenging but has much better control over things than Luban does.
It could also be this:
Gaps Between Infill and Outline (simplify3d.com)
This site here is a great reference for learning to fine tune things…
Print Quality Guide (simplify3d.com)
Try to practice printing a calibration cube, such as this:
XYZ 20mm Calibration Cube by iDig3Dprinting - Thingiverse
This allows you to see how things are going, while also giving you something measurable to figure out how dimensionally accurate you are currently printing.