It's hard to say as the image is very small, but looking at the external walls, it could be under extruding.

As a newbie, I am presuming you have not yet heard or learned about calibrating the extruder. It's not a dig we have all been there at some point.

I have posted a few links below that I have written that you may find useful.

Start with PID Tuning the heating element
PID Tuning Extruder Calibration

Then do the bed (You might as well while you are at it, it is worth doing)
Heated Bed PID Calibration

Then calibrate the extruder motor
Calibrating Your Filament Extruder

Hope it helps you out