Rayon does have tremendous amount of stretch especially along the bias. If you ever make a rayon skirt or dress, definitely let it hang before hemming.

Sometimes, iron on interfacing can stretch or shrink fabrics, like the heat and water and fabric combo don't always play nice.

My aunt used to hand baste seams before sewing them which always seemed like so much extra time to me. I, also, sometimes skip staystitching. With some fabrics, though, hand basting and stay stitching makes a lot more sense.