Was there a mistake in my prayer, and did I fall short in praying sufficiently, and what was the mistake I made? Will Allah answer me if I pray to die and meet Him, after my desired prayer was not answered?

A servant must have a good opinion of his Lord, even if he is denied something he hoped for. Sometimes, denial is a blessing, and granting can be a tribulation. Not achieving what is desired might be a kindness from God, for the All-Kind to His servants may test them with what they dislike to elevate their ranks and ward off harm from them.

Not achieving what is desired does not mean you have erred, although sins can be a cause of tribulation.

As for wishing for death, it is forbidden. And whoever wishes to supplicate, let him say: "O Allah, grant me life as long as life is better for me, and take my soul if death is better for me," because a righteous Muslim may increase in good deeds, and an evildoer may repent.