It's ok.. did not found any errors in the first run, only some grammar mistakes but that can be fixed easily.
I got a question, do you make the dorsal beams active at some point?, cause they would harm to those GTVA vessels and the point of dissabling those is exactly to save the ships, if you didn't you can script something for that...
Also you could try doing the mission a little more harder... like adding more shivan warships or wings, maybe a cain escorting that ravanna.. it just feels so "not shivan" seeing it so alone....
other than that it's a decent first mission indeed.. keep going and try doing harder stuff ^^
EDIT:
check the starting ships.. you say Alpha will fly bombers but the default ship for alpha wing is a perseus.