When you are creating your template, are you creating multiple sheets under the worksheet section?
I just did a quick test and I was able to create an excel report with two sheets. I would make sure that you have multiple sheets created in your template, and I would also make sure you are retrieving your template correctly. There is a button called “create report” that you can use to test with.
Hope this helps!
Edit: Are you using the same input object for both sheets. Do these two fields match on both your sheets?