Your calculations are pretty much meaningless. Orbital mechanics is not that simple.
Here's the path we actually used to send an orbiter to Mercury. Interestingly, it did a bit of solar sailing to make some fine adjustments to its trajectory by angling its sun shield.
More direct transfers are possible, but they require more dV on the spacecraft, and the rocket equation means increasing dV increases the ratio of fuel mass to craft mass exponentially.
Here's the path we actually used to send an orbiter to Mercury. Interestingly, it did a bit of solar sailing to make some fine adjustments to its trajectory by angling its sun shield.
http://www.theplanetstoday.com/messenger_flight_path.html
More direct transfers are possible, but they require more dV on the spacecraft, and the rocket equation means increasing dV increases the ratio of fuel mass to craft mass exponentially.