It's a very good game with well-made level design, I hope you will even make a sequel of it, but you need to fix some things, -1 star because of these important flaws.
1. As @yound pointed out the game fails to award the medals and you need to place something like a "re-send medals" button, but in the way that would NOT HARM the achievements data stored on players' computers. The game owes me medals for completing the game and picking up all collectibles. It is a classic problem of the game getting disconnected from NG API after a while.
2. Also like @JeffreyDriver wrote the game is completely not saving progress. No matter how many levels you pass when you click on "continue" you have to play from the very beginning.
And to even underline it once again: when you will be making updates for the game be sure not to mess with the users' data, so they would not have to replay the whole game again to get their medals.