if you got a film, you did not clean off the remaining soap properly, keep cleaning and it will be good. But if you got glass, then you shouldn't need to worry about that for a while. I like the ability to remove the plate and flex it to pop off a print, so mine is getting a spring steel plate soon.

As far as glass being a different height in the middle, glass is supposed to prevent that. But yes, you could try shimming it with tin foil or something similar so that it transfers the heat.