It has been proven many times that germans were nowhere near getting an actual bomb. In fact, they never were able to devise a successful method for uranium enrichment.
Part of the problem was lack of resources. While raw uranium was plentiful, the heavy water was not. The only plant that was producing something close to the neede amount was in Norway. In fact, at the time it was the only plant in the world that produced heavy water of 99% purity. Supplies of it, were nowhere near what german scientists were demanding. The Norway plant was continuously sabotaged by the local Resistance as well as britsh bomping raids. The only other plant that could provide some amounts of heavy water was in Italy, but the best they could do was ~10% purity.
Another problem was that there was no centralised research effort. Several competing groups of scientists worked on their own projects, refusing to collaborate and help each other out. Since they worked under different patrons, such as Wermacht, Luftwaffe, SS, they were also forbidden from sharing any information with other groups. Interestingly enough, even Reich Postmaster sponsored a nuclear research lab.
There is another theory as to why germans never succeeded. It was rumored that most scientists simply sabotaged research to the point where it appeared that they are making progress (to protect themselves) but intentionally not getting close enough to the point where uranium could be enriched weapon's grade.