Hi there,
It sounds like the usage details in Screen Time don't appear to be correct, is that right? We'd love to look into this with you.
Just to clarify, is the issue only with Instagram? In other words, does the usage for other applications appear to be correct?
You mentioned that you closed Instagram; can you let us know more about how you closed that application? For example, did you switch apps using the App Switcher, or did you force close it using these steps? How to force an app to close on your iPhone, iPad, or iPod touch
Also, to help us narrow this down further, can you confirm which iOS version your device is running at this time? Here's how to check: Find the software version on your iPhone, iPad, or iPod
In the meantime, you can find some great information about Screen Time here: Use Screen Time on your iPhone, iPad, or iPod touch
Thanks!