Retrieving a deleted layer

Thanks for the responses. I have closed and reopened, so I will not be able to retrieve it I guess. So let me ask another question... I was at work today and opened a Ps document that someone else had created. I don't know what I did (because I'm a relatively new Ps user) and I don't even know how I ended up saving it. The document is floor plans overlayed on a site plan with logos, text, etc. (i.e. too complicated and too many layers for me to be able to re-import the source document and re-format the entire thing.) When I first opened the document, all the floor plans looked normal. But now, one no longer has a white background. The black outlines of the rooms are still there, but there's nothing underneath (I see the gray & white checkerboard background between the black outlines). I need to know how to make that area white again. It seems to me like maybe what happened was I deleted a layer...maybe...?? I can't just use the fill tool to fill white into the background space because (a) the entire shape is not closed, so applying fill to one area fills the entire document and (b) I know that's not the right way to do it... I'm trying to get it back to the way it's supposed to be, not just make it look like it's right when it prints because other people from work may still use the file electronically. Please let me know if you can help!