Suggestion:

Showing your enthusiam/interest is  more important than your technical capability. Here are two key points might help you during on-site interview:

Key Point No. One:   Show them that you really like them and you want to work with them ("OMG, these are just the exactly right people I want to work with.....")

Key Point No. Two: Show that you really want this job and want to STAY there....

Smile.... talk about family, hobbies, events..... be a great listener.....

It won't always work out for you, but it will help.