HAMBURG (Reuters) - Returning to her birthplace, Chancellor Angela Merkel urged supporters to mobilize undecided voters before Sunday s election, telling them not to take her conservatives  solid lead in opinion polls for granted. Surveys show many voters are still undecided and, with the election likely to return a fractured parliament, she wants to maximize support to bolster her position in coalition negotiations.  What I ve heard in the last days is unbelievable ... that everything is already decided,  the 63-year-old told a crowd of several hundred packed into the Fish Auction Hall in Hamburg.  It is not. Every vote counts!  Noting that the center-left Social Democrats (SPD), her closest rivals, have not ruled out a left-wing coalition with the Left party and the environmentalist Greens - a tie-up untested at national level - Merkel added:  We live in turbulent times. We can t afford any experiments.    In these times, we need stability and security, and a clear path, both at home and abroad,  she said. Before Merkel spoke in Hamburg, a band pumped up the crowd, belting out  Celebration  by Kool & The Gang and Bryan Adams   Summer Of  69 . One or two greying supporters stood up and danced. SPD leader Martin Schulz told broadcaster RTL he believed there could still be a last-minute swing in his party s favor.  The experience of all elections, national or international, show that the number of undecided people is growing more and more,  Schulz said.  Everything is still possible.  A win for him would be against the run of the opinion polls. On Tuesday, a weekly survey conducted by Forsa showed support for Merkel s CDU/CSU bloc - known as the  Union  - at 36 percent, its lowest since April, but still far ahead of the SPD, on 23 percent. Attention in Germany is largely turning to who Merkel will govern with after the election, rather than whether she will stay in power. Latest surveys suggest that only another grand coalition of Merkel s conservatives with the SPD or a nationwide untested three-way  Jamaica  alliance of the conservatives, FDP and Greens would have a stable majority. A coalition involving the FDP could limit her room for maneuver on pressing ahead with euro zone reform. Without detailing how she wanted to develop the EU, Merkel delivered an impassioned defense of the European project, saying she regretted Britons  vote to leave the bloc.  I could stand here and talk for hours about how arduous Europe often is,  she said, before adding:  It always is worth standing up for Europe, even just because it gives us peace and freedom.  