Fill not working?

Having lots of trouble trying to fill shapes! what and I doing wrong? I draw a circle, hit fill and the whole page fills, fast mode is unticked. I have changed threshold, grow and feathering are all small values or zero, nothing works?
I’d like to be able to create layers for each colour based on filling parts of line art, but with fill not working very frustrating.
Any help would be appreciated.

First of all are you trying to use it on the same layer you did the circle or on another layer? If it’s on another layer you need to change the samples to all layers. Also make sure your threshold value is low i have mine at 3. And you probably will want to set grow selection to 1 or 2 pixels to avoid gaps.

Other than that you might want to check the colorize mask too. And make sure you have no gaps in your lineart.