We have identified a problem where in certain specific cases, the app does not unlock. The fix is in the works and will be available as an App update shortly.
Meanwhile there is a workaround.
If the start button with concentric circles is white it means that the App is still Locked. If the Start button is yellow it means that app is unlocked.
Now in your case I assume the Start button is white so you can follow these steps.
1) Click on Start. Then click on Week 2
2) You should see the Get Full Version button. Click on that.
3) Click on Restore and download. If you have made a purchase previously Apple will detect your purchase.
4) Once you download, Click Open. This will incorrectly still bring you to the locked app.
5) Open Week 1.
6) Now we need to reopen the app. So you can click the Back button on the top till you get to the Download/Open screen again.
7) Once you open the title a second time you should see the yellow start button.