I try so hard to concentrate that I end up fighting my own thoughts the whole prayer and feel exhausted and defeated. Am I doing khushu wrong?

You are not doing khushu wrong. You are doing it as a battle, and that is why you finish the prayer worn out.

You have imagined that presence of heart means seizing every wandering thought and wrestling it to the ground. But it is not a fist. It is closer to the hand of a mother who draws the child back, again and again, without anger. Each time you notice the mind has drifted and you quietly return, that returning is itself the worship. You did not fail a hundred times. You turned back to Allah a hundred times, and He loves those who turn back.

Ease is built into the very floor of the religion. Allah does not stand over you asking of a tired body a perfection it cannot give.

“Allah does not burden a soul beyond its capacity.”

Qur’an, Al-Baqarah 2:286 · meaning

And our scholars have always held out this mercy, so take it in full: a thought that arrives uninvited carries no blame. Not a trace of sin attaches to it. You were never asked to keep the mind empty, because that has been asked of no one. What is asked of you is the gentle return, and it is that return, repeated, which is written down for you as worship.

See how the Prophet (peace be upon him) dealt with a worshipper whose eyes were closing during the night prayer. He did not tell him to push through.

“When one of you becomes drowsy in prayer, let him sleep until he knows what he is reciting.”

The Prophet (peace be upon him), Sahih al-Bukhari (213) · meaning

These words are about drowsiness, about the one whose sleep has grown so heavy that he no longer knows what his tongue is saying, and they are not a licence to let an obligatory prayer slip past its time whenever we feel tired or unfocused. But look at the spirit inside them. If the religion is this gentle with a sleepy worshipper, it is not harsh with a tired mind that strains only out of love. Our masters of the Naqshbandi-Mujaddidi path have said the same for centuries: presence deepens through soft return, never through force. Straining to empty the mind only stirs it more, the way pressing on water only scatters it.

So put the sword down. Come to your prayer as you would come to sit with a Friend who is merciful, and when the mind slips off to your worries, bring it home without scolding it. That homecoming, repeated with patience, is the khushu you were afraid you had lost.

One small step: In your next prayer, choose one thing to return to each time the mind wanders, perhaps the meaning of “Allahu Akbar,” and let every return be quiet, with not a single word of rebuke to yourself.