Crochet projects can be curled in many ways. If the tension is too tight, the fabric will stretch and curl. Make sure you don't pull the thread too tight and consider using a larger hook. Uneven stitching or the wrong number of stitches can cause curling, especially if the number of stitches is increased or decreased. For example, if the flatness is not high enough, it may cause it to curve into the bowl. Finally, some stitches, such as Tunisian crochet, have a natural bend. Gluing, wetting, and shaping the finished product can help reduce frizz.