That is the whole point of an IVA - you agree an affordable amount to pay for 5 years after which time your debt will be cleared, whether you have paid the full amount owed or not.
You usually pay only a percentage of what you owe in total.
How come you are having problems keeping up the repayments, have your circumstances changed since taking out the IVA?
If the IVA fails, you will probably find that most of the money you have paid so far will have disappeared in fees to the company managing your IVA, therefore you may find that your actual debt hasn't done down by much, if at all.
Your creditors will then want full payment of the debt rather than a percentage (like was agreed in the IVA) and you may find yourself being bombarded with letters etc from debt collection agencies.
I would suggest you post full details of your circumstances on the Money Saving Expert website - they have an IVA board and the people on there really know their stuff and will be able to advise properly.
Go
here and register!