A little hint. I see that you don't have access to a router. So, to make those edges and general layout a little cleaner (good first stab BTW), swing by my shop next time and buy a yard of thin foam backing. You can adhere the vinyl to it and the foam to the box and it will cover any imperfections and make the overall job look really professional.

I have also seen some DIYers just cover over carpet with the vinyl with suprisingly good results also.