I have just made this in illustrator. I made a path and used gradient across the stroke, but this highlighted area appeared. So, how can I fix it using photoshop or illustrator ?
It's a fiddly try, but it doesn't look so bad:
1) I copied the horizontal path protruding to the left. You need to know the height of the path (which you can calculate based on the stroke size). Create a rectangle of the same height.
2) Change the width of the rectangle in half.
3) Apply the same gradient to the fill, and clear the outline stroke to 0pt. Use "Linear" and an angle of 90 degrees.
4) Alter the path of the rectangle into a triangle, where the tip would be pointing to the right, down.
5) Copy said triangle, mirror it vertically.
6) Play with the width (50% should do).
Then adjust your horizontal path in your initial picture, so that it does not overlap with the bow, and take your triangle to cover it. Makes even a nice 3D effect.
Here's a detail of the triangles overlapping the paths, with a black outline:
A detailed view of the "fiddly joint":
This is a possible final view:
By changing the right side of the triangle into curves, you may make it even look better and more "3d-ish".