Can you extend your own life with the death note?
No, because of several things:


A human with the Shinigami Eyes cannot see the lifespan of other Death Note owners. (How to Use: XVIII)
If you write your name and a cause that cannot be possible (being stabbed by a dead man), you will die of a heart attack. (How to Use: LV)
Writing your own name in the death note bypasses all lifespan calculations. If you wrote that you die at a certain date, you will die at a certain date, regardless of how much lifespan you have remaining.