state space model in 'm' script

i have a historical data(numerical data) of 8 inputs and one output.i designed a state space model using the command 'ssest'.Got 'A','B','C','D' and X1,X2,X3 (3 states for our numerical data) parameters.after i try to do prediction using this parameters..but i'm stuck with how to make the formula(in matlab script) for multi input single output using state equation and output equation...

how to handle the 3 states to get single output from y..and doubt in... i have 8 inputs so that should i create 8 state equation ? like y=cX!+cX2...cX8...but this shows wrong prediction...please help me what is the correct way to do prediction using state space model when we have 3 states and 8 inputs and one output? ..my output should be within some particular range...example:- 100-120..

please tell me the right approch about how to do prediction in state space model in 'm' script for multi input single output?

i attached exaple dataset and code i tried to prediction..when i was design a MPC in script step by step..