What zone are you in? I would say plant more, water well and wait. Select plants for your area. Monkey grass, smaller daylilies, etc. Eventually you should be able to remove the plastic, or replace it with bricks, stones, etc.

I think once the grass grows in you will be fine.

Or more pavers (like the ones on the patio) used as the border if you want to accentuate it more.

@HALLETT & Co. i was thinking the same thing. Im hoping the border wont be so obvious.

i dont bother with plastic edging or stone anymore. just get a garden edging spade/ shovel like the fiskars square garden spade ($30) and in spring make a nice edge and use a string trimmer to keep it nice all summer. Its simple, no need to buy edging and looks clean.