The 'lumps' you speak of are a predicted result of inflationary Big Bang theory, which predicted specifically that the background radiation, while generally in the smooth form of a uniform blackbody spectrum, would have very small anisotropies. They were subsequently found.
Add to that that the BB properly predicts the observed ratios of hydrogen to helium in the universe (and more recently, even lithium), and there's actually pretty outstanding support for the theory.