Tawhid (Arabic: توحيد tawḥīd, meaning "oneness [of God]" also romanized as tawheed, touheed, or tevhid) is the indivisible oneness concept of monotheism in Islam. Tawhid is the religion's central and single-most important concept, upon which a Muslim's entire faith rests. It unequivocally holds that God is One (Al-ʾAḥad) and Single (Al-Wāḥid); therefore, the Islamic belief in God is considered Unitarian."Tawhid constitutes the foremost article of the Muslim profession of faith.
Tawheed means not believing nor worshiping but only Allah (SWT). Shirk is believing or worshiping other than Allah with Allah (SWT). We believe that the Prophet and his Ahlul Bayt are the most humble servants of Allah.
Prostrating at the doorstep of the Prophet (SAWA) is in fact for thanking Allah for granting us the great bounty of visiting the shrine of the Prophet (SAWA) or his Ahlul Bayt (AS). Thanking Allah in the form of prostrating is a sincere worship to Allah and can never be Shirk. We never believe nor accept any claim suggesting worshiping the Prophet, his Ahlul Bayt or any one but only Allah (SWT). Respecting the Prophet and his Ahlul Bayt does not mean worshipping them at all. Respect is completely different from worshiping. Wahhabis mix wrongly between respect and worship. Even we prostrate at the doorstep of the holy shrines, we never do it as a sign of respect but we do it as an act of thanking Allah for His great bounties on us.
Thank you for your question. Shirk is to limit Allah in any way such that even the conception of another god would be possible. Even to say He is a god is not satisfactory as that would entail a genus of gods under which God would be a species with only one referent. Numerical oneness is limited, as in numbering God as one a person gives the possibility of two gods. Numbers themselves are a factor of the material world. Rather, Allah is above being numbered as a number entails a limit and He is above all limitations.
As for prostration, it is clear that if a person prostrates to a being in worship then that is completely forbidden in Islam and Shiism as a sect within Islam. However, prostration does not only entail this meaning and is also a symbol of humbleness. For this reason God commanded the angels to prostrate to Adam (as), not in worship or out of polytheistic intent. So too Prophet Ya'qub (as) prostrated in front of Prophet Yusuf (as).
May you always be successful
If you repeated the wrong words of others with out intention of its meanings of Shirk, you are not a Mushrik. Your faith is what is in your heart. Still you need to repeat Estighfaar for saying something wrong.
There are no other gods to show envy towards them.! We know one God, if there is more than that they (Hindu) should prove it.