Your answer is probably correct to an order of magnitude, but this type of question ("probability of skipping last n whatevers out of N total whatevers") is nigh impossible to answer completely correctly.
Consider the following similar question: let's say I'm a CFOP user and I don't do any multislotting. What's the probability of skipping the last slot (out of four slots, total) when solving F2L? The naïve answer is 1/15 (corner) × 1/10 (edge) = 1/150, but this is wrong. Last slot skips are much...
