U is potential energy, not total. It's defined right there in the, um, definitions. Total is K+U. That's making the rest of your math jumbled. Also things with subscript 2 correspond with position C, not B. Also there are two separate scenarios; the first on the flat plane where potential energy stays the same, and the second up the incline where potential energy increases.
All that aside, you still didn't say what part of my post that bears on, or how it bears on it.