The short answer would be a no. No, you are not a Christian because you go to church on Sundays. However, let us unpack why, according to the Holy Scriptures.

First, Romans 3:23 teaches that all have sinned and have fallen short of the glory of God.

Notice that it says ‘all,’ meaning everyone since Adam and Eve have sinned with the exception of Jesus the Christ.

Now, Romans 6:23 says that the wages of sin is death but the gift of God is eternal life through Christ Jesus our Lord. If all have sinned as stated in Rom. 3:23 and the wages of sin is death, then we all have earned the wages of sin which is eternal death in the lake of fire.

But the wonderful second part of 6:23 is that the gift of God is eternal life through Christ Jesus our Lord. Salvation can be received through believing in the death, burial and resurrection of the Messiah.

Jesus says in John 14:6 that He is the way, the truth and the life, no one comes to the father but by Him, Salvation has always been through faith in the God of Abraham, Isaac and Jacob but since His first advent, salvation is now exclusively through faith in the Godman Yeshua the Messiah; the second person of the Triune God. Acts 4:12 confirms this, referring to Jesus it states. And in none other is there salvation: for neither is there any other name under heaven, that is given among men, wherein we must be saved.
Jesus in John 3:3-6 states that you must be born again, one is born of water, meaning your natural birth but then to receive salvation and become a Christian one must be born again in the spirit. This is the second birth which results in salvation and baptism into the body of Christ; the Invisible or Universal Church, Ephesians 4:4-6.

Now that one has become a Christian by putting our trust in the death, burial and resurrection of the Messiah, I Corinthians 15:1-8; we can now obey the ordinance taught in Hebrews 10:25, to not neglect the gathering of the brethren.

So in summary, you are not a Christian because you go to church, but once you have become a Christian by putting your faith in the death, burial and resurrection of Jesus the Messiah then you should obey the ordinance to fellowship in a local church. We are saved by grace through faith (Eph. 2:8) and not by attending church.