I pick 2 bubbles to check from each lesson. I do not tell the kids which ones I am going to look at, I do that on my own. Anyhow, by doing that, the kids have no idea which 2 bubbles I am going to grade so in order for them to get credit they have to complete them. If they do not have those bubbles completed, they get a zero, even if they have all of the others completed. If they do something wrong on the puzzle, I write a comment in the online gradebook and allow them to fix the problem. When they do, they have to resubmit (on Google Classroom) and I go back to give credit. I know it sounds like tons of work, but my students have learned so much this way. It allows them to see what they did wrong and correct it so that when they get to the final project they can actually create the game.
In addition to this, on the Free Plays at the end, I give a separate grade for. I give them specific criteria that I want to see in their free play. I always use some of the code from that lesson, but I also give criteria from previous lessons so they get more practice. I have found (now that I am at lesson 21 of unit 3) that the students really know what is going on. I think if I didn't do that, they would not understand how to write the code as well.