You can try converting to a black and white bitmap and then re-trace it sometimes that helps flatten the image and make it two colors instead of many different colors of black and white
See this threadIm trying to trace a piece of artwork that a customer has on his t shirts and when i send it to corel 4 and trace it some parts come out shaded ,so i didnt know if i have to convert it to bitmap or which trace option would be best suited for this black and white artwork?thanks Gary