It's important to remember that this phrase is quite literal and doesn't necessarily imply a negative connotation. "Baja" is a feminine adjective meaning "short" in Spanish.
Here's a breakdown:
* Yo: I
* soy: am
* baja: short (feminine)
If you want to say "I am tall" in Spanish, you would use "Yo soy alta/alto", with "alta" being used for a female speaker and "alto" for a male speaker.