You have two options when crowdfunding with us to either 'Keep what your raise' or only receive 'All or nothing'.
All or nothing – If you don't hit your project's target, then no money will be taken from your supporters. Your backers will receive an email informing them that the project has not reached its target and that they will not be charged. You'll not be charged any fees if an 'All or nothing' project does not reach it's target.
Keep what you raise – You will receive any funds pledged on your project regardless of whether you reach your target or not and you'll be charged the fees on all pledges received (which will have been removed before the funds reach your account).