It's happened to all of us at one time or other who paint our homes. Those little swatches we choose of color can sure surprise us can't they?!
In your situation you can try a simple decorative painting technique listed at the website below or you can mix the yellow color of paint with some white paint to make a color you like and then just paint one wall that will help your room seem larger. (you can also just buy a lighter color you know you'll like with the walls).
The lighter wall can really be a Godsend in view of walls that are "shouting" their color at you. I know I would try this before repainting everything.
Helping the room seem larger is important. Using very light colored curtains/drapes,if any can help too. I know it's wierd but the more "outdoors" you let in the larger the room will seem too and the brilliant yellow can be dimmed a bit through this.
There's a ton of help here.I think I'd choose "Better Homes and Gardens Decorative Painting" where you can turn those walls into blessings !
I hope everything turns out really well !