Currently, you don't need to complete all stars to obtain the final achievement. If you didn't get this achievement before because some levels weren't given full stars, you can obtain it by logging in to the game again. (Fix some minor bugs)
Reduced the difficulty of the last achievement
Source: Steam Community (opens in a new tab)
Build and release context
Recorded Steam release date:
Within one calendar day of this post (UTC). The listed date does not establish an exact launch time.