Decimal spacing in SSRS report

Hi,

I have text box on ssrs report where expression is :

=Sum(Fields!DebitBalanceMST.Value) + Sum(Fields!CreditBalanceMST.Value) like this but  amount

of type:6034.89 is printing ,but when it has just 399 it printing default ..but i need it to be print as 399.00...

i did all modification on textbox prop like use 1000 separator and format(=Sum(Fields!DebitBalanceMST.Value) + Sum(Fields!CreditBalanceMST.Value) ,"0.00") but of no use...please help me on this