If i remember correctly if you do not reach the exit you want due to whatever you can cancel the ticket and redo it.if you know what i mean.
Yes, you cancel it using the machine. It may be possible to get it refunded to the card but if it is then I never worked out how to do that, for me it has just spat out two tickets same as maut tickets then you just take them to the till in the Rasthof etc and get the refund in cash. There’s a cancellation fee, might be 1.50 euros?
Thanks Harry. 
Yes you can cancel it and it costs 3 euro’s to do so. 