This question already has an answer here:
I am trying to make a 3D brick wall to fit in a certain shape. I have made a brick pattern > expanded it > used the perspective grid tool for perspective (I have also tried warping). Once I have the perspective I want, it seems like I am unable to edit the shape no matter what I do and when I use the knife I see this weird selection, it is much bigger than my shape (see picture). I can adjust the shape through transforming as well, but I need it to fit into a predetermined shape. I have the room created, but I want to put bricks on the wall and I am trying not to recreate the whole room.
What do I do?