Without going into a list of things and sounding like im telling you what to do, the scope is kinda an arbitrary thing. How much you literally can do in a week is the theoretical maximum scope and what you chose to do is the actual game scope. If you think of an idea bigger than what you can do in a week, you wont finish, and if you have an idea smaller than what you can do in a week, what do you do with the time you have to work on the project?
Theres some more practical tips like make a single screen or single level game, or start with a easy to make player controller and then find the first thing you can do thats on theme for the game. Use free assets for things you dont want to make. I dont like making music so i team up or find free to use music online for my games.