1. Your top rail is probably a lot longer than you need. I think most can get by with 10-12 feet for a normal gathered end hammock (most only need 10). You can probably get a ballpark number if you use dejoha's hang calculator and futz with it until you get a decent idea.
2. Don't connect your hammock to the end cap. If you look at my original post the hammock attachment point is almost in line (vertically) with the top rail attachment (I didn't know it at the time but that was the correct way to do it). People stopped doing the end cap thing (probably the wrong way to do it... at least for most) a long time ago when they figured out that connecting to the end cap causes it to bow (and possibly fail) or connecting it closer between where your top rail is attached will cause the rail to sag (and possibly fail). hppyfngy has a very good method that he has been suggesting for use. It might be in his signature (not sure). You could also do something similar to what I did in the original post... whatever works for you. But get the hammock attachment in line vertically with all of the other stuff. Hinge/shackle attachment, toprail attachment, hammock attachment... all in line vertically (or as close as possible).
Found it! This is about the best way that I can think of to do it, the hppyfngy way ...