In a Rut

Molly you're in a tough spot, and I get it. I'd stick with what you are doing, but consider adding an element of gamification. Remember that gamification is not necessarily about adding games (although it could include that) but about adding a series of rewards that motivate the participants.

For example, you may already ask course participants to answer questions either within a module or at the end of a module. Build on that by offering a badge or part of a badge for each right question or each module passed. Tell them at the beginning that their goal is to "earn all 5 badges" or "earn all pieces to create the final seal of approval" or whatever makes the most sense for your course. 

Instead of badges they might be earning points, or revealing a portion of the course certificate, or a lot of different things. You can get really fancy, but you don't have to. Keep it simple and build on what you are already doing. 

There are also lots of free templates you can find on this site that have pre-built interactions and games. Perhaps you can use one of those so you don't have to spend time building your own.