compare your sketch with post #8. Do you see the difference?
What commands have to be used for sending one SMS and did you really use all of them in your sketch for the second SMS?
Generally speaking:
Before changing any program make sure that you understand every line and command in the original.
Don't make too big steps. Start with the blink example, understand it, change it (fast/ slow blinking, morsing ...) instead of starting with sending a SMS