The facts are against you, scripture repeatedly references the FIRST day of the week as the day important events happened (penecost, the resurection, etc), the day the apostles preached, and the day they came together to break bread.
If you’re doing these on a day which ain’t the first of the week (Sunday) you are doing contrary to what the Bible instructs.
The facts are not against me. The scriptures enforce the observance of Sabbath for the Christian because Christianity is the continuance of the Hebrew faith. We worship the same God, and in many aspects, in the same manner. The Christian is grafted into the Hebrew vine, not the other way around.