When I opt into beta, mine is 0.3.6. When I opt out of beta, I get 0.3.5b. Is there something wrong with my account? I've also noticed that other people online (mainly Youtube) have said that they don't have 0.4.5 either.
Op out of the betas and then go into properties and Verify cache. It should download what you need.
by doing that you let steam check to see if your copy matches theirs, and adds what you are missing.