Unfortunately, once you sent a photo sharing request to your friends, they will receive a push notification instantly, which cannot be canceled on the app - otherwise, it may cause confusion to the receivers.
After the receiver accepted your request, you could change the photo-sharing status as follows:
- Go to Friends (2nd tab, bottom menu)
- Tap your friend
- Tap the avatar icon
- Find Photo Sharing
- Tap Active to change the status