Pick up the background color, it looks green? And have it reduced by 50% for your wall color, it will be very pretty.

It's a Kelly green. What type of throw pillows would you use. Can I bring in gray?

I would use yellow and white throw pillows, perhaps one in blue. Gray? A blue gray area rug might work, I'd have to see the two together. Or perhaps this one: [houzz=]

I like the idea of the green walls. I think the sofa will blend in nicely. What other color could you use? Pink Walls? Yellow walls? I don't think they would look good. And white would be blah. I think the background green in a lighter shade is the way to go. I would decide on the curtains after I painted the wall, then you can get some at the store and hold them up to see how they look. White would be safe. Maybe a yellow to match the throw pillow.

yellow walls with blue curtains. go neutral on the floor and solid on the pillows.

How can I give it a more romantic look? I think I would go for pale yellow walls, crisp white shutters, and maybe cover a chair in drop clothe ruffled on the bottom.

Not a mistake at all, the sectional is perfect for your cottage style and a bargain of a lifetime at $200! The colors you should use are all right there in the sofa fabric - shades of pink and red, yellow, and blue. Using paler shades, or slightly grayed down or otherwise shifted, will update them. Walls could be pale ashy green, pale ashy blue, creamy white, or even an icy chalky white. Curtains should be solid, stripe, or check with scale of detail either much smaller or much bigger than your floral. Wild card accent could be orange.

I'm not sure what romantic means to you, but to me, the sweet floral already has a lot of feminine charm. Along with obvious accents in same vein, I would be looking for 1 or 2 pieces that are rustic, bulky, industrial, or otherwise masculine in nature to balance the sweetness.

Emerald is Pantone's color of the year (2013) so I think you are right on target.