you should be able to put it there. save the game a couple times just to be safe. then flatten the ground where the canal part you want goes. if you have NECORA's riffle mod ,you can use that to make slopes down 3/4 a tile depth. you can use CC terraform to go 1 and 2 tile depth.they do help with the canals to dig out around them once they are built. sometimes to place these, i do have to turn the screen and zoom in.computer likes to push the curser,so you might be overlapping more than needed. trick is to flatten only as much as you need for the piece. the other terraform tools do help dig around them where they meet the lakes.