Freezing, or not reacting physically, is a really common response to sexual violence. People respond to an assault in different ways.
Just because you didn’t resist physically doesn’t mean it wasn’t rape – in fact, many victims make the good judgment that physical resistance would cause the attacker to become more violent. Lack of consent can be express (saying “no”) or it can be implied from the circumstances (for example, if you were under the legal age of consent, or if you had a mental incapacity, or if you were afraid to object because the perpetrator threatened you with serious physical injury).
Although it can feel as though your body has let you down, it has done what it can to keep you safe. Sexual violence against you is never your fault.