Hi,
There are two things which can cost you. one is interest and the second is penalty.
1. Interest
Interest in case of non-deduction of TDS – Interest shall be levied @1% for every month or part of the month from the date on which TDS was deductible till the date on which TDS actually deducted.
Thus, you should deduct and deposit the tds ASAP. Post that file TDS return as well.
2. Penalty
Maximum penalty for non deduction can be equivalent to the amount of TDS. However, its not automatic and tax officer has to initiate the penalty. If you voluntary pay the tds now and comply with the provisions, chances are that penalty should not be levied.