Boost converter output power issue
The control topology of your chosen device is a strange one, and often difficult to analyze. It seems as the device operates far outside of the continuous conduction mode (CCM), and starts, what the data sheet calls, "Burst Mode operation". I guess it is some kind of pulse frequency modulation with constant on and off time until the output reaches some kind of threshold voltage.

What I can guesstimate from the datasheet is that in this burst mode the switching transistor is turned on for 3.9 us and turns of for 0.7 us. Your inductance current will peak over 1.482 A, which is beyond what your inductance is rated for (550 mA). My guess is that your loss in efficiency is in the inductor.

A few things worth mentioning:


You are searching for the loss of what I would say is a modest amount of power (~200 mW). It is often a complicated task to design highly efficient switched mode power supplies at light loads.
Your electrolytic capacitors are rated far beyond what you need for this application. You only need 16 V capacitors. Yours are rated at 450 V. They will have a significant ESR (which is not good)
A good design measure is to also add small ceramic capacitors at the input and output of the converter, as they have far less ESR than electrolytic (which will increase the converter stability and efficiency.
I would recommend to replace all your electrolytic capacitors with ceramic, and decrease your 100 uF capacitors to maybe 10 or 22 uF.