In your first column of power calculations, the formula is correct but you must have made a mistake in the spreadsheet calculation. Either that or you didn't take into account the the probe gives Vpeak not Vrms so it must be converted.
This is shown correctly in the second column formula: your reading squared divided by 100. In converting Vpeak to Vrms you divide by the square root of 2. However, since this is subsequently being squared, you can just put that in the divisor with the 50 and that makes it 100.
Of course both voltage measurements should have the diode voltage drop correction added back in before and any calculations are done.
Be aware that dummy loads/detectors can be built in different configurations so the formulas may vary (e.g. Elecraft's DL1 where the probe is measuring across only half the load).
PS: What is a VMM?