I am not that great at giving directions but here goes!!
When I decide to do a wrap around binding, I....VERY CAREFULLY....trim off the excess batting to the edge of the quilt top....BE SURE....to pin the backing fabric away or you will cut into it and then have to do a regular binding!!!
Then I lay out the backing fabric and using my straight edge ruler and rotary cutter, I trim the fabric to at least 2 inches and sometimes 2 1/2 inches all the way around. Now, fold your backing fabric in half ( more or less....no rules here!! ) and tuck it back into the quilt sandwich and fold the edge over and either finish by hand or machine. Corners are a bit tricky but practice and you will get it....the time saved in cutting the binding and sewing it on will give you the extra time to fold and tuck those corners....but really, they are not that hard.
I've found that by cutting extra backing fabric and folding it over before stitching the binding down, will give me a good sturdy binding that will last as long as a seperate binding...IMO!!
jodi