Cant Make Filled Region Small Enough

I have been making a very low resolution game, I mean it to look like a 90s or 80s game,
but because of its low resolution (just a little smaller than a GP2x screen) I can't make the filled region small enough!
Is there anything that can be done?
but because of its low resolution (just a little smaller than a GP2x screen) I can't make the filled region small enough!

Is there anything that can be done?