Using the snap to line up your pieces is WAY easier and much more accurate. Well actually its perfectly accurate. I know it can be a little weird sometimes but there is a method to the madness. What I like to do is make sure the coordinates for all the floor pieces are whole numbers and keep the snap to 1. What this does is ensure all floor pieces are aligned with the world grid and will allow you to line them up perfectly. Doing it by freehand is what causes those "invisible walls" that sometimes happens where your ball suddenly stops on what appears to be smooth ground. There might be like 0.01 misalignment between two floor pieces which looks good by eye, but the ball can hit it still since its not connected smoothly.