There are times that I think I just want to throw my painting away.
I as an artist am my own worst critic. Even with a well thought out plan
for your image, things can go south.
Time has taught me though, that if I walk away from that piece moving on to
another one, I can go back and tackle that feeling in different ways once I
look it over again.
I can yes of course throw it away, I can keep it around for reference as what
not to do, or I can use a surface preparation medium to change just enough of
the work to correct or change what was bothering me about the piece.
There are times I accomplished this, by using the same gesso I use to prep the
painting itself. There is one I particularly like to use called
Liquitex Professional Gesso Surface Prep Medium, Clear, 32-oz.
It has a gritty feeling that the paint adheres to well.
If I am working on a canvas or even a heavyweight paper I'll also use
Liquitex 5321 Professional Matte Gel Medium, 8-oz, 8 oz, Clear
to layer the paint giving it an impasto look.
Here is an example of how I altered the part of an acrylic painting I was not happy
with.
If you want a more precise line change you can also get the painters tape,
like the Artist Tape on the left of this page.
You will also see a book listed there, I think is a how-to paint
in acrylics reference.
Happy Painting. :)