Hello,

so after completing the first part of the storyline, i accadently hit Preston Garvey and now he is the objective to follow, but when i go near him he turns red and tries to kill me, everytime i kill him, he goes back as the objective as a green color. But when i go near him again he goes red and tries to kill me while Mama murphy walk around as if its normal, this is outside the Museum of Freedom

Any help would be useful.

That must svck but you are lucky that mission is only about 30 minutes in. So if it's that bad, you can just restart the play through.

Also always make sure to save a lot before approaching people, areas etc so you can reload the last save if something went wrong.