There are two options you can use.
If you are sending push notifications via the API, you can use the Android Style "Big Text". This would allow you to be able to send more text within the alert itself.
Otherwise, your only other option is to test and make sure your message is not being truncated by modifying the text of the alert that you're sending.
Alternatively, you could choose to send the text of the alert in either the summary or title fields of the Android Notification to be able to have the user see the entire text when they pull down on the notification.
I would recommend testing out the Optional Features that are displayed to you when creating a push, and seeing which option works best for your use case.