Hm, it looks correct. I do not know what you have exactly hoped for, but if I would give you this pieces as paper cutouts and told you to place them in a rectangle form without squashing, rescaling and only in 90° rotation steps (these are the conditions you have set for the program to work with) you or any other software would not get any other much better result.
This is the combination, under to rule-set you defined, is almost the best result that can exist.
You can maybe try to set smaller rotation angles and with “Ø” 360° rotation steps; this way you may get few additional percent more. 60% ±5 what you have now is very likely the optimum, there is nothing wrong in the solution you have.
You will notice that the big isles are what define the space usage. They can not be better packed, they already fill all possible space. The small stuff has just filled the holes, with small isles you can’t save no more space - the large one are decisive in your project.