@El-Jefe got the rules correct. To give it a tad more context, I'll offer this.
Mats are expensive. While the NCAA would prefer that every institution uses a larger mat (52X52), they don't want to force smaller programs to have to purchase a new mat. Plus, they are aware that some smaller arenas, where some of the smaller programs compete, really don't have enough space for 52x52, plus the required 5 feet from the edge of the mat to anything (tables, bleachers, wrestler seating, walls) that could be considered dangerous to the competitors. So, they've been forced to compromise, and provide minimum and maximum sizes of mats, so that all NCAA programs can use their existing maps, and hope that if/when they purchase their next map, they'll purchase a larger one (if the arena/competition site allows for such).
Mat costs, and competition site limitations, are an even bigger issue in high schools and middle schools. That's why the out-of-bound rules that the NCAA adopted were slow to be (and still not fully) adopted by the NFHS, which sets rules for high school & middle school.