How to predict using state space model identified using system identification? (to be used in excel)

Hello All, I am a beginner and I have used experimental data (4 inputs and 1 output) from an exothermic reactor to identify the model of the system. I used system identification tool and obtained the following state space model. However I am unable to use it effectively in excel. How do I do the step wise calculations in excel? I tried simplt substituting the values in an excel table, but I get no fit with actual values and the error keeps increasing exponentially!

x(t+Ts) = A x(t) + B u(t) + K e(t)

y(t) = C x(t) + D u(t) + e(t)

where,

A is

                        x1           x2           x3           x4
           x1      0.99912   -0.0070421  -0.00031249  7.7892e-005
           x2    -0.063971      0.83586      0.32571     -0.29828
           x3    -0.021337    -0.074777      0.87549      0.53156
           x4   -0.0010908       0.1197     0.061085      0.60444

B is

                  u1          u2            u3            u4
           x1  1.7668e-007 -8.4364e-008  1.3983e-006  9.3092e-006
           x2   -1.22e-005  6.8841e-005    0.0036294    0.0055134
           x3  4.7894e-005  1.6459e-005    0.0055848     0.012066
           x4 -3.8301e-005  8.3878e-005   -0.0018173   -0.0067679

C is

                        x1           x2           x3           x4
         temp       866.56      -2.8526     -0.48543       0.3932

D is

                     u1            u2            u3            u4
         temp            0            0            0            0

K is

                      temp
           x1    0.0016648
           x2      -0.2073
           x3    -0.087051
           x4     0.025893

and x(0) is

           x1     0.088771
           x2      0.27148
           x3     -0.62389
           x4      -1.4389

Estimated using N4SID from data set of 8 merged experiments

Loss function 0.00272453 and FPE 0.00279113

Sampling interval: 1

In Matlab the model shows a good fit of close to 92% for 1 step prediction. However when I try to manually check the same in excel I am getting no fit. The first 5 predictions are close to actual values, but the error keeps increasing exponentially.

Where am I going wrong? Please help!