I'm not sure what you mean by "curve". By definition, cross-stitch is "block" by the use of straight stitches and blocks of "x"s.
You can do curves by a lot of short backstitches that look like a curve from a distance or possibly the use of couching and putting the connectors in a way that looks curved.
Thanks. I use this to make crochet charts for crochet picture blankets. I was making a circle image and needed to add font on the inside of the circle and curve the font so it goes inside circle
You need to do such things as stitch at different angles as you crochet in a circle? There's no way that this software can handle that. The closest it can handle crochet is as filet crochet.