Did you head back up to the pyramids? They're up in the upper left hand corner. The sunflower is down in the lower(ish) right. After you put something on the x, you have to walk back up to the pyramids and enter the floating light thingy. You'll know it when you see it. :) This gives you a chance to pick something else up before you switch levels. If it's still not working, you might want to reload the game - it might be buggy.