Hello Abhilash B:
The 10 samples will keep get repeated, until you manually stop the program (they will be transmitted over again and again without a pause, until you stop the program). The 20MHz sampling rate will determine the output speed (DAC samp rate) of your SDR - assuming that the sampling rate of your SDR sink block is set to 'samp_rate'. If you did not use the samp_rate variable block anywhere in your flow graph, it simply does nothing.
Please note that USRP uses I-Q sampling; you should feed in complex numbers, instead of the real float. Also, I do not know how your 'dat' file is structured - it should contain raw IEEE754 single precision numbers (something to double check if your program misbehaves).
Regards,