lxterminal doesn't provide any options for maximizing window, so you may want to consider using another terminal application that provide this option, like
Or you can add these lines into applications section inside ~/.config/openbox/rc.xml
but every instance of lxterminal would be maximized by default.
P.S. Another solution is using wmctrl program inside your script, for example:
wmctrl -r :ACTIVE: -b add,maximized_vert,maximized_horz
# your script start here
# end of the script