I am afraid the game you purchased is patched, hence it will NOT work for the downgrade.
Whereabouts did you buy it anyway?
Apparently Japan versions of Lumines have been patched. Don´t know about other areas.
(...) Is there a way I can still downgrade? Please help. (...)
Well, you will have to give us information before we can try to help you such as the firmware version installed in your PSP. We can´t read minds, you know?

(...) When will there be a 3.50 downgrader that doesn't need lumines? (...)
When will I win the lottery? Would you be able to answer me? I guess it´s the same here for your question.