Hi, Bedrockjulie---
I figure you either already got past this level or deleted the app from your phone out of frustration, seeing as you posted in December and it's now June.
Getting the first block of the tower is the tricky part to me. After I got that one cleared, the others cleared more easily.
You need detonate two star gems together at the top of the gravel column to start the process. I found the easiest way to get the star gems created was this process:
1. Build a star gem using the two lower left chambers.
2. Use the lower left chambers to position the star gem immediately before the left jet.
3. Shoot the star gem over to the right jet.
4. Shoot the star gem up into the upper right chamber using the right jet.
5. Slide the star gem to the left, and then drop it on top of the gravel blocks.
6. Repeat the process for a second star gem.
7. Detonate the two star gems together. This clears the top gravel block.
I hope this helps. Good luck!