It appears you are not producing a sine wave but driving some kind of square wave to the MOSFETS. I assume you are using a center-tapped iron cored output transformer with some DC votage applied at the center and the MOSFETS go to the ends of the windings. If I'm right, you have three electrolytic capacitors across each side of the transformer drive signal which is probably not a good idea, especially as they appear to be reversed polarity. Please show where the connectors go to and the type of transformer you are using.
Brian.