If you're planning to use the touchpad on your laptop to write, although this is possible, we do recommend trying to get hold of a mouse if you can, as it will make things easier for you (it may be worth asking your school or somebody you know if you can borrow a mouse).
If the touchpad is all you have available, be aware that it would be fine to tell your interviewer verbally what you want to write (and get them to write it for you) if you are struggling.