Something like this only happens once in your life,
one shot at the time. There has to be an angle.
Does this mean that there's got to be a way to achieve/obtain something or
that it is too good to be true and that there has to be a catch.
Your first option is correct.
When you say "there's got to be an angle", it implies that the "way to achieve" what you want to achieve may be unusual, or ingenious, or obscure, or unexpected.