Why my printer leaves small lumps/bits on surface

[ASP]

I have printed a bed levelling square to demonstrate the things which I want to explain. The surface of my parts is always having small bits/lumps of materials?



Is it problem with material flow rate? My ultimaker 2 plus asks value for material flow rate in %, what should be the value?



P.S.- I have tried levelling the build plate but it's not the solution to my problem I believe. Thanks

[Bikeracer2020]

A picture of the bed leveling square would help to see the surface. The 'Z' offset might need adjusting in the slicer settings.
I don't use Cura, however a guess of 100% is a figure to start from and adjust in small increments.

Orca, Bambu and Prusa slicers use the figure of '1' as a starting point, a flow rate setting might be between '0.95' and '1'