Not uncommon to find scummy things on the top of a primary fermentation (or even a secondary for that matter). Leaving the hops in there could have caused it but tough to say. The bottom line is not what it LOOKS like, it's what it TASTES like. If the sample you tasted didn't have any off flavors (band-aid like, creamed corn, vegetal, cidery, cardboard, etc) then don't start worrying. Bottle it, see how it turns out and enjoy it if it's good.
As Charlie says: "Relax, don't worry..."
On a side note, I have a lot of friend brewers who use plastic fermenters but I noticed the quality of my beer went way up when I switched to glass and even more so when I switched to using stainless fermenters. Don't get me wrong, if you treat your plastic fermenter properly (don't use scotch bright or anything else to clean the inside that will scratch it) they you should have good luck with it.
BTW, a great option to chemicals for cleaning fermenters is good old boiling water!
-Kev