Question:
Is my prayer valid, if I lost concentration when making takbir and did not prostrate for forgetfulness?
Answer:
In the Name of Allah, the Most Merciful and Compassionate
If you pronounced the name of Allah Most High whilst in your heart you knew you were entering the prayer, the prayer has commenced. [Tahtawi/Shurunbulali, Hashiyat Maraqi al-Falah]
Your gaze and concentration do not affect the validity of the prayer and therefore do not require any prostration of forgetfulness. [Ibid.]
Advice
I would strongly recommend brushing up on your basic Islamic jurisprudence. Knowledge is a great tool to prevent confusion and uncertainty in issues such as these.
Consider the basic fiqh classes offered here at www.seekersguidance.org
I hope this helps,
Allah knows best.
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani