Is it mandatory to show fd tds in itr

you have to disclose all your income in ITR, hence TDS also u should disclose to get the credit

And bigger question, what if I don't show it?

if u wont show tds then u wont get the credit,say for example u hv gross total income of 600000,which includes fd income of say 50000,on which tds of  5000 is deducted,so ur total tax liability is may b around 51500 less tds of 5000=46500,if u wont show tds then u wont get credit of Rs 5000 and u'll end up paying tax of 51500.............................hope its clear...........................

while filling itr,u got to write interest from fd in other sources which will increase ur income by amount of interest on fd,mention tds details and then ur net tax payable will b tax on taxable income which includes interest from fd less 3470.

it will b like

1.income under the head salary  - 497970

2.income from other sources         -interest from fd

3.gross total income                        -497970+interest from fd

4.less : deductions

5.net taxable income                         497970+interst from fd-deductions

6.tax due on net taxable income         after applying slab rate on net taxable income

7.less :tds                                            3470 +tds on salary

net tax liability                                    6-7

and in ur case ur salary is less than Rs.500000,so if u wont show interest on fd then u need not file itr................but then u wont b able to take credit of tds on fd....................

In case you do not have any tax liability, and still bank has deducted TDS from your FD interest, you will get the refund from the IT dept because you have technically paid tax when you were not required to pay. Why give up the refund which you may receive by showng the TDS in ITR? 

And if there is a tax liability, the TDS deducted by bank will reduce your tax liability accordingly.