butt cutt is where you take the flap of excess and cut it flush to the rest of the carpet with scissors?
Easiest way to describe it:
where two flaps or ends meet, lay both flaps down where you want them to end up, one on top of the other and then cut thru BOTH pieces at the same time. Peel back the top layer then remove the excess from the bottom layer and lay the top piece down again. Since you cut BOTH pieces at the same time they should meet each other perfectly where you cut. You should be using a razor knife or boxcutter, not scissors. All cuts should be made while the carpet is glued to the box.
It sounds like you are trying to cut "patterns" and then attach it to the box when in reality you want to glue the carpet down to the box as you go and cut it immediately before the spray glue dries completely with a box or carpet knife.
Spray glue one large side, attach the carpet...spray the next large side..wrap the carpet around...flip the box...spray the third side...wrap carpet again...spray the forth side...wrap the carpet. This should all be one continious piece of carpet, no cuts yet. Now you're back to the first side correct? This where you KEEP wrapping from the fourth side OVER the first side.. The first side should have two layers now...here comes the butt cut I explained...cut thru BOTH layers down to the wood...peel back the top layer and remove the small, now unattached piece from the bottom layer...then carefully lay the top layer back down so it BUTTS against the bottom layer making a perfect seam.
It harder to explain the ends. It much better to actually see someone else do it. But here it goes:
You should have left enough excess width at the start to fold over the ends. This is where you want to think like a Christmas or Birthday present. Spray glue the end of the box. Start folding the excess carpet over the end one side at a time. You're going to have to make cuts from each corner outward to make each piece lay flat. Now you'll notice that each piece will overlap the other...this is where you want to make more butt cuts until each piece lays perfectly flat with each other. When all the glue finally dried you can rub the carpet around the cuts to make the pile of the carpet blend together, hiding the seam even more. If you do it right you'll have to look real close to find your seams.
I don't know if that will help. I'm not good at typing out instructions. Sorry.