Of course, Arun, you need to surrender monies not used, if its "On Account/Advance Basis" basis. Usually these are given as petty cash given for business visits to meet its expenses.
Besides, also note that there is a policy called "Per diem basis". If you were paid the allowance on "Per diem basis", all the you have saved is your income. Enjoy it. Also, remember, such money will have to account it as a part of your income declaration for taxation purpose, since you have stayed aboard only for 45 days.
9th July 2013 From Saudi Arabia, Riyadh