Considering the fact that NIFTY has had very sharp runup of more than 12% in a very short span of time it is highly unlikely that the index will jump another 6% in a month without spending time in consolidation. Also 5650 would be a significant resistance for the index considering the fact that the index has been making lower tops and lower bottom since 5th November 2010 and 5650 was the recent top made by the index (see the nifty ladder analysis here).
Assuming 2 lot of NIFTY (1 lot = 50 NIFTY) is sold at Rs. 13
Total premium collected = 100 * 13 = Rs. 1300
Total Transaction cost assuming Brokerage cost including STT and other taxes at Rs. 50 per lot = Rs. 100
Margin money required: Rs. 39,900 (7% of total call value)
Total return = 1200 / 39,900 = 3.0 % in 25 days