Like the others have said, welcome to the forum.
There are several factors that go into how much force you put on a hammock suspension that may explain why you got by with crappy rope. First, I bet you weren't using a ridgeline...that reduces the angle, thereby increasing the force on the supports. Second, I bet you didn't sleep in the hammock...stretch over an hour may not put your butt on the ground, but let it stretch over a night and you may end up scraping your butt on a rock, rubbing a hole in your hammock (or at least getting it muddy).
But regardless, most folks say to get webbing or cord rated for at least 700lbs or so. Remember - knots greatly reduce the working load of cord, and even moreso for webbing. That's why sewing is better for webbing, IMO. When I broke the 550 cord, it broke right at the knot.
Personally, I wouldn't use webbing from a fabric store unless it came with a tested working load. The risk of falling in some of the places I hang is greater than the benefit I get from saving a few days of shipping when I order webbing from Ed Speer (plus I get to support a great guy's business - www.speerhammocks.com)
. YMMV - just be sure to test it carefully before you trust it to hanging over sharp rocks or on a steep ridge.
You can usually find load-tested Spectra at climbing shops, kitesurfing/sailing shops, etc. Climbing shops usually carry nylon webbing instead of polyester. It'll work, but as mentioned above it'll stretch...and to get nylon webbing strong enough that it won't stretch too much overnight, it'll be much heavier than polyester. But it'll work.
Let us know what you decide...and most importantly, have fun with it.