I am painting the walls in a papered room with Dulux Walls and Ceiling paint. After doing one wall, I can see strips of overlapping paint from top to bottom where I have completed one length and gone on to the next which is spoiling the finished job. Is there any way I can prevent this happening? Am I putting too much paint on although it doesn't look like it? It is a large, cool room and I cannot go any faster so any suggestions would be most welcome. Thank you.