Barbra,
When I apply the pattern at scale of about 40%, I get definite lines like
a grid. <<
That’s inherent in that particular pattern, and can happen for two different reasons. One is if the pattern does not tile seamlessly – that is the left and right sides (or the top and bottom) do not create a continuous pattern when joined. That can often be cured by using the Offset filter with wraparound and the clone tool to ensure edges will match
The other is when the centre of the tile and the edges of the tile are distinctly different, because then, although the tiles may join seamlessly, there will be a distinct pattern of tiles