By Tom Miles GENEVA, Sept 4 (Reuters) - talks aimed at uniting Libya's two warring governments are entering the final stretch and there is hope of signing a deal on Sept. 20, the U.N. Special Representative for Libya Bernardi** Leon said on Friday. "We really have a chance to reach a final agreement in the coming days and we can**t afford, Libya can**t afford, to miss this opportunity," Leon told reporters. Leon met negotiators from Libya's General National Congress (GNC) for five hours on Friday and said he expected to hold a new round of talks next Wednesday, which diplomats said would take place in Skhirat in Morocco.