Best way to offer team member help?

I've been having a problem recently. In my recent sprints, I have found myself finishing my work well before the sprint ends (several hours in a 2 week sprint).

I am left with a lot of time and nothing to work on. I approach my team members and ask them if I can help them, but they always refuse.

I am bored during this time, and need something to do. If I finish my work early, I would like to help other people who are still working.

Is there any way I can get them to accept help so I have something to work on?

Thanks