Hi, welcome to the Sony Forums 
Are you seeing any 'buffer overflow' messages before the camera stops recording?
Try recording to a memory card instead of the internal memory. If you are already using a memory card, make sure it is a genuine branded card with a fast write speed.
If you want to combine the clips you already have, you can use PlayMemories Home (that came with the camera) to edit your clips into one long movie: http://www.sony.ie/hub/playmemories
Cheers
Mick