Do not beat yourself up if when you are painting it does not go as planned.
Clean the layer and start again.
With this I always draw the sketch layer separate to the painted layer, this way you will not loose everything.
At times its takes me 3/4 re-paints to get a descent form of the face etc, or even complete redo of the entire piece.
If you are not feeling it, don't force finish it, try painting it again, you never know you might find the form you imagined
I do this more then I care to admit.
(For the month of Ramadan I will post random tips that I struggle with to show you are not alone)