Hey there, I'm one of the artist that worked on Target: Unknown. To answer your question if you bet the game.....No. You got close though. There are at least 4 levels.
Keep trying :D
Dev here - sorry for the long wait and lack of communication!
Although there's not a lot of reference to it in the game or on the page, the game is an endless arcade game similar to other retro titles such as Space Invaders or Asteroids. The game does not have a true 'end', instead the objective is to beat as many levels as possible and increase your score :)
However; you did beat all the levels, which is really impressive. Personally I still consider the game to be in an unfinished state, and it may be worked on more in the future. Story mode may indeed become a fully fledged story with an ending and more levels.
If you have any questions or confusion I'm more than happy to answer them and help out :) Thanks for playing!
- Jukey