Brush tool tip is very big - please help

Hello,

I am unable to draw using the brush. My tool tip is very big while the line itself is set to be thin. Once I leave the pen button the line becomes OK.

I have attached two images:
before I leave the pen and after.

Please help I am desperate already …
Thanks a bunch

harmony brush.jpg

harmony brush after.jpg

Does this also happen in a brand new project?
Are you zoomed-in at all?
What are your brush settings?