Do I need to confess my sin to a scholar or a pir for my tawbah to be accepted, or can I go straight to Allah alone?

You can go straight to Him, right now, with no one standing between you and His door. In our way, the way of the Naqshbandi masters, a teacher is a lamp for the traveller and a companion on the road, and that is a real help, but he is never a gate your repentance must pass through. Forgiveness belongs to Allah alone, and He hands that key to no one else.

You need no one to carry your sorrow upward. The One you are turning to is nearer to you than the veins of your own neck. The Qur’an settles the matter in a single question.

“And who forgives sins except Allah?”

Qur’an, Al-Imran 3:135 · meaning

There is only one answer to it, and that answer is Him. No scholar, no guide, no pir claims this station, and the truest among them are the first to point you past themselves to your Lord.

“It is He who accepts repentance from His servants.”

Qur’an, Ash-Shura 42:25 · meaning

Notice the words, from His servants. Directly, with nothing in between. He receives your turning Himself, into His own care. Your private whisper in the dark reaches Him unmediated, and He is not too great to lean toward the smallest sigh of the one who returns.

So do not let shyness, or a sense of unworthiness, persuade you that you must first find the right person before you may approach. Many people carry that habit of thinking, and the Book lifts it off the shoulders. Go as you are, in your own words, in your own language. A wise guide, if you have one, only helps you walk this road with more steadiness, he never stands where only your Lord may stand.

One small step: Right now, wherever you are, turn to Allah in your own plain words, just one sentence of return, without waiting for anyone else, and know that it has already reached Him.