Interesting that the phase 1 burnout occured higher and faster than you anticipated, but by the time it got to 3.2 km it was travelling significantly slower than predicted. From that it seems as though thrust was much higher than anticipated, but so was drag.
Since you ignite phase 2 at 3200m, I assume the fairly long coast period is by design, what's the rationale there? For instance, would it not perform better if the coast was much shorter, but the phase 1 thrust were lower? Gravity drag would be a bit higher, but it seems as though it's the aero drag killing you.