Okay, you have a new mask, but how are you going to manage the drop shadow without seams?  Here we go!
 

Step 1
Open a new image.  Width should be 1025 if you intend to use it for a web page;  height is important later on, so remember it.  I'm using 50 because I had to use SOMETHING.

Step 2
Flood fill the new image with a tileable pattern, tileable gradient or solid color.
Next, apply the mask  (you probably didn't name your mask "tug" so choose whatever you did name it!)

Step 3
Why DID I  name it "tug"?  Because I was tugging at the straight lined edge to get the curve, of course!  LOL
After applying the mask, you want to delete the masked area by deleting the mask;  click yes to merge.
                 
 

Step 4
Can minimize that image and create a new one now.
This time the image will be the same width but the height will be 600 pixels to get a good tiling (Why 600?  Because it's large enough to show any flaws.)  Great size to do deskchecking but in this tutorial we are not just deskchecking - this is where we apply a drop shadow that will tile well.

Step 5
Set you flood fill pattern to the image you just masked, the flood fill the new image (should have a side border all the way down it.

Step 6
Apply a drop shadow at any horizontal setting you find appropriate,  andy opacity you like and and blur setting you like but keep the vertical setting  at 0.

 

Step 7
Using the rectangle selection tool with 'anti-alias' unchecked, start at any height you want in the curve and at 0 (first set of parenthesis) and drag the selection past the right end of the image and to a total height of 200 pixels (third set of parenthesis).
This image is 1025 wide, so 1050 means I'm past the end of it which means it is all included in the crop zone.

formula reads:
start drag point to stop drag point = dimensional size of image crop line (sorry - don't know that last one!)
*NOTES*
Coordinances in lower left hand corner:
left number in parenthesis is horizontal and right number is vertical;
first set of parenthesis is where I started my crop;  the horizontal is 0 and the vertical doesn't matter;
the second set of parenthesis is where I have dragged to;
the third set of parenthesis is the size I have selected.
never bothered to find out what was in the brackets;  probably something important that I would use if I knew!  LOL
For this tutorial, the important part is the 1st and 3rd set of parenthesis in that I want to make sure I start at 0 on the left and I want to drag clear over to the right edge and I want the selection to be 200 pixels tall for exact tiling because the mask was made to be 200 and the new image where I applied the mask was a percentage of that height - therefore, my finished height has to be a multiple of both.

Step 8
Next, crop to selection.  This gives you your perfect tileable image.

Step 9
To finish up your Tug, add a new raster layer.
                        

Step 10
The new layer will be on top;  in the Layer Palette click and drag it to the bottom as shown in the two images below.

Step 11
Once the new layer is on the bottom, choose a basic background tile pattern, tileable gradient or a solid color and flood fill the layer;  then Merge/Merge all.  Your side border is now ready to trim ala your creative mind.
 

*NOTES*
The mask height was 200 pixels;  tile was made with a beginning of a 50 pixel height flooded into a 600 pixel height, cropped to a 200 pixel height per the tutorial above.

The mask height was 200 pixels;  tile was made with a beginning of a 100 pixel height flooded into a 600 pixel height, cropped to a 200 pixel height.

The mask height was 200 pixels;  tile was made with a beginning of a 200 pixel height flooded into a 600 pixel height, cropped to a 200 pixel height per the tutorial above.

 

Close Window when Finished.