Is string theory really science? According to Karl Popper's theory of demarcation, science should be falsifiable but string theory is yet to be tested experimentally as It will require at least 19 TeV of energy to prove it which is not possible at this moment of time so Is string theory really a science? 
 A: 
According to Karl Popper's theory of demarcation, science should be falsifiable 

Is Karl Popper the pope of science?

but string theory is yet to be tested experimentally as It will require at least 19 TeV of energy to prove it

You are wrong on two counts: a) a  physics theory is never proven , only validated or falsified and b) you are assuming that string effects appear only at 19TeV, again from some Papal dicta.
I can assure you that there exists various phenomenological models of string theory  that predict effects from string theory at the energies of the present LHC  not to mention that finding supersymmetry would be another major breakthrough towards validation

Is string theory really a science?

String theory is not a science . It is a theoretical model which aims at unifying all known interactions in physics. Whether it will be validated or falsified lies in future experiments but that does not mean it is a useless exercise. It already has the mathematical structure to embed the standard model of particle physics and this in a sense is a validation. It is a necessary condition for any theory aiming at unification of the four forces. 
Edit in order to expand the last paragraph because the question "is string theory ...." appears often here, in various forms.
When the first atomic spectra appeared the regularity of their distribution was mathematically modeled with the Balmer  series very successfully and let into classifying atomic spectra with series. 

Balmer's equation inspired the Rydberg equation as a generalization of it, and this in turn led physicists to find the Lyman, Paschen, and Brackett series which predicted other absorption/emission lines of hydrogen found outside the visible spectrum.

This eventually led to the Bohr model of the atom , a step forward in theoretical analysis, but not definitive. The great progress was made when the Schrodinger solution of the Hydrogen atom displayed the Balmer etc series, and quantum mechanics theory took off. If the quantum mechanical equations had not come out with the  series as solutions , they would have been falsified.
Elementary particle physics  data is much more complicated for simple series fits to it, waiting for a theoretical model.The data are fitted onto the standard model which displays a striking group symmetry, as striking as any series , the SU(3)xSU(2)xU(1) group structure  which is imposed on the standard model lagrangian by hand more or less. 
In this sense the Standard Model is equivalent to the Bohr model for atomic physics data. The striking group structure is expected to come out naturally from any theory of everything, TOE.. 
If the SU(3)xSU(2)xU(1) group structure is not in proposals for a TOE, the proposed theory is falsified/rejected as a candidate for TOE in the same way that the Rydberg-formula series  falsify any alternatives to quantum mechanic theories if they could not come up with them in the solutions.
