Instead of asking people on AAM to speculate why dont you ring your bank and ask it to send you up to date redemption figures including any early redemption penalty. Then you will know for sure.
you will be lucky to owe them less than you borrowed particulalry after breaking out of a 5 year deal so early. In essence you asked the bank to borrow money for you for 5 years and now you have changed your mind. All comes at a cost. I know its obvious but try and keep the house if you can
Impossible to tell without knowing your fixed rate. If it's only a 5 year mortgage you may already have enough equity to cover the shortfall - although as the previous poster said, there may be penalties involved. Do you have a copy of your mortgage agreement?
Your bigger problem may be actually getting the house sold
Have you considered renting the house out? It is definitely not the time to be selling but as the others said contact the bank for redemption figures etc.