Find out what's using the most space. My guess would be music and sound files. If that's the case, try re-encoding them at a lower quality, for example, using mono instead of stereo.
If you have a lot of graphics, try exporting with lossy compression. It’s not like JPEG, and it won’t ruin your pixel art. Chances are, you won’t even notice the difference.
Another option is to export with PNG images and then compress them using Pngquant. Again, you likely won’t see any visual difference, but image sizes can be reduced by 30–50%.