The Zn half is:
Zn ==> Zn^+2 + 2e
The NO3^- half is"
10H^+ + 8e + 2NO3^- ==> N2O + 5H2O
Multiply the Zn half by 4, the NO3^- half by 1 and add the two equations.
I have 5 for H2O also.
If you will type your equation in I will tell you why it is wrong. I know you can look at your answer and compare it with mine and see where the coefficients are not the same; however, it is possible to balance the equation atom for atom and even electron for electron and NOT be balanced.