Video Timeline help--please help!

I'm trying to insert a video of me scrolling through a website which is 15 seconds.  These mockups which are still objects show them at 5 seconds, so when I insert my video, it goes blank after 5 seconds. 

I'm assuming it has  something to do with the ipad/laptop being 5 seconds-it won't let me drag them out in length either.

I have been trying to figure this out for HOURS, if anyone can help, you would be my HERO!!!!