My mother died in New York without a will her and my stepfather own the house together am I entitled to a percentage of what the house is worth?

If the deed says husband and wife as owners, you are not entitled to anything.  The property passes by operation of law.

Maybe. If they bought the house before they were married and did not specify "joint tenants with rights of survivorship" on the deed you're entitled to your mother's half, split equally with any siblings. But if the deed says joint tenants, tenants by the entirety, or husband and wife (if purchased during the marriage) your stepfather gets her share. If she left any other assets you're entitled to share them equally with your other siblings after your stepfather gets the first  $50,000 or one third, which ever is greater.