What do you need to do once you finish quilting your fiber art piece? You should be blocking it to straighten edges and flatten the ripples if there are any, and there usually are some! Hopefully you have quilted your piece so that there are not large areas of unquiltedness. You should aim for the same density of quilting overall. If it’s a large piece you can pin it to a rug and mist it with water, making sure the corners are square. Then simply let it dry. This can take a while depending on the humidity. A small piece can be pinned to a design wall or piece of foam core. Then mist with water and let dry. Make sure if you want your edges square that you pin them like that or they will dry wonky. Sometimes I will hit the edges or bindings with my steam iron with a piece of muslin on top and really flatten those edges. I don’t like to flatten my quilting too much so if I iron the middle, I will hover the iron over the surface and just blast with steam. I know there are lots of other methods out there if you consult basic quilting books, but these methods have worked well for me in the past.
A small piece pinned to my design wall, which is BTW large pieces of insulation board nailed to the wall and covered with black felt.