Do the two pieces of the 6' x 7'6" mat have beveled edges on all four sides? If you lay the two pieces side by side, is there a gap in the middle due to the beveled edge?

No, the two pieces of the 6' x 7'6" mat are not beveled on all 4-sides, just on three. One side of each mat will have interlocking teeth that will allow you to interlock the two pieces together to create one large mat. These mats interlock very tightly, giving you a virtually seamless appearance.