"Squaring up" can have different meanings, depending on the stage of the quilt. Has your top already been quilted? Has it been bound? Is it out of square? What exactly are you trying to do?
If it is a top that has not been quilted, or a quilted top that has not yet yet been trimmed and bound, then you need only to measure to see whether the top is square, mark the lines to be cut, and then you can trim using a cutting board on your dining table. If your quilt has already been quilted and bound and you need to square it up by blocking it, then you really need to be able to stretch the whole quilt out, while it is damp, and secure the edges with pins to a carpet or cork board or something like that. I don't think that part can be done successfully unless the whole quilt is stretched out.