No, the fill is not a seamless texture. Was never meant to be seamless - having been made as a background piece for a full size GIMP map in the first place
It is, however, large enough, even at half the original size, to fill the entire polygon on the map in one piece without pixelating, which is what I attempted to describe above... or maybe that was a description I gave over at Profantasy Forum?
Storm - if you decide to go ahead and still use the parchment, please use the 4000 x 2500 version I sent to you - the landscape piece, and set the fill scale to either x=4000, y=2500, or if that is simply too large, x=2000, y=1250. Either way, it needs to be large enough for the parchment to fill the polygon on your map all in one piece, since those lines are not folds
If you decide to use something else instead please do. I won't be offended. I was merely offering a possible solution