You don't get to choose the purpose. The purpose is the activity, the purpose of life is living it. Like making music, the purpose is the activity of playing. Fulfilled, you aren't expected to do anything extra and so the option of a choice isn't required. The free-will is now, this part. The meaning is up to you.
You have control to create life, your free will spawns a new human with free will. However we do not control the abstract thing that is "living" we are bound into it, the decisions that were made that created you were not yours to make. You didn't exist.
You are a part of a system, you are a piston meant for firing in an engine that needs every single part. If you leave the engine and try and look at it from an abstract view your absence stops combustion and it no longer becomes an engine. You must exist as a part of it, if you didn't it wouldn't be.