Some of the undecided SPD voters have come back and that is what has given them the extra three points. We'll have to wait to see if they can hold on to them.
Voters would like to keep Schroeder but they consider the SPD incapable of governing the country.
Even though there are probably a lot of nonvoters among the people who are undecided, this proportion of uncertain voters indicates continuing movement even shortly before the election.
Even if many of the undecided end up not voting, this share of 'don't knows' suggests voters are still wavering right up to the election.