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I can't see enough of the canvas or image in your screenshot, to be able to gather all the info I would need to find the problem. Can you share the SVG file?
Briefly, what I want to look for, is whether you have all the "spokes" crossed over at the center of each line. And I would also want to confirm that they are all at 15 degrees rotated from each other.
A simple solution to your problem would be to extend the spokes outward, which makes the ends further apart, and the arcs would fit. Since I can't see the whole image, I'm only guessing here. But I'm guessing that the arcs did fit on one side of the web, but they aren't fitting on the other. If that's the case, then extending the spokes longer won't fix the whole problem.
Or another simple solution would be to just scale the arcs smaller until they fit. Still not ideal though.
However, as we often find with Inkscape, there are a few, or sometimes even several ways to approach a particular goal. Here's how I would make a spider web.
1 -- Enable the Star/Polygon tool
2 -- Set it for 24 Corners (on the control bar) (24 corners makes 15° angles)
3 -- Draw the star to whatever diameter or width you want
4 -- Adjust the Spoke Ratio, until it's pretty close to the shape you want for the arcs, even though they will be sharp and not curved (probably it will be something like 0.920 to 0.960)
5 -- When the whole thing is as close as you can get it, except for the sharp corner of the arcs, do Path menu > Object to Path. (Make sure everything is right, because after this, you can't adjust it as a star shape anymore.)
6 -- Switch to the Node tool, and you will see that there is a node at each corner around the original star
7 -- While holding the Shift key, click once on each of the internal or concave corner nodes
8 -- When they are all selected, change them to smooth nodes, which is this button on the Node tool control bar
9 -- Ta-Daaaah!
10 -- Now switch to the Pen or Pencil tool, and draw the spoke lines. If you use Snapping, it will be easy to make sure they are all placed well. Do you need info on snapping? You can draw a line from one outer or convex point, to the one on the opposite side or the original star. That will cause them to automatically cross in the middle.
11 -- Now switch to the Selection tool and select the outer web line
12 -- Duplicate
13 -- While holding Shift and Ctrl keys at the same time, grab one of the arrows with the mouse and drag inward
14 -- When that line is where you want it, just stop dragging and release the mouse
(Edit - if you want these lines to be some specific distance apart, you'll want to use Object menu > Transform > Scale, so that you can scale them by some particular amount, rather just visually estimate the size)
15 -- Repeat #11 through #14, until you have enough lines
16 -- I would select the whole thing, in the end, and Group everything together, to make sure it doesn't come apart when you move it. But really, it's optional. Or you could use Path menu > Combine instead. There's a little difference between grouping and combining, but in this case, the main point is to keep all the pieces together.
I realize that spiders don't make webs exactly like this. It would make a much more complicated tutorial to make a web in the way the spiders actually make them. It could be done, for sure, but it would take a lot more time and details.
