It is very common for actors and dancers to visit my singing studio and make declarations such as:
"I'm not a singer, I'm much more a dancer"
"I'm a trained actor, I don't really sing"
"I was always weakest at singing"
Then guess what... they sing REALLY well... and many times if they hand't told me they're "not a singer" I wouldn't have thought it.
Many students in training make these kind of decisions early on and then identify with them throughout the following years and the rest of their lives. It's a way to feel safe and part of a tribe. It's a way to diminish further what we already feel weak at - it's the "you can't get me world, I've already put it out there" thing we all do when we are fearful or vulnerable. The danger is it can become a self fulfilling prophecy, and quite sub-consciously we can take this attitude into auditions, meetings, agencies and eventually on to stage.
Time and time again people who think they can't sing or will never be able to sing astonish me with what they can accomplish. Students start out with no singing voice whatsoever and go on to to play only leading vocalist roles by the time they leave training. It's incredible what we can achieve if we only believe in ourselves.
My advice to you today is to keep an open mind, don't put yourself in a box (too many other people in the industry do that for us already) and believe that you can achieve anything.
Lots of Love