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A word of caution: you need to check the instructions on the yarn label before using water, heat or steam on your crocheted pieces. If heat or steam is not recommended, then an alternative is to smooth out the pieces, pin them down into the shape desired, and lightly spray the pieces with water or cover with a damp cloth, then put a plastic sheet on top, then some equally-weighted heavy books on top of the plastic. Let the pieces dry naturally overnight. Your pieces now should not be curling. They should be shaped as intended and ready to be sewn together.