It's okay, It was probably the pressure of exam/test conditions. You're not alone - A LOT of people end up doing that under stress in tests. How much was it worth? Listening tasks are usually given a very low weighting (5%-10% is the common range in my experience). Just don't let it bother you - there's no point stressing when you can't change it, so just work to get the best marks you can in the next assessment task.