I came out to my parents months ago but they don't seem to pay any attention to what my gender is each day - they always use my birth name and male pronouns despite me telling them that when I'm wearing this necklace I'm a girl and they should use female pronouns. I don't know what to do, I keep trying to correct them but I'm always too scared. I keep getting angry when I want "girly things" but they won't let me have them. Have they forgotten or what?
Well if you have come out and they took it well reminding them should be enough. But since they won't let you have "girl-stuff" the problem probably lies more within them not being accepting or not taking you seriously. If they aren't accepting there isn't really anything you can do and coming out a second time wouldn't really change anything. If they didn't take you serious try to get across how important this whole thing is to you and that you are in fact very serious about it.
I doubt that they've forgotten. Even if it were months ago, they may still be processing it or in denial. I came out to my parents more than 2 years ago and they don't use he/him.
This is my best bet, actually. Binary trans people have recognition to a large extent now, more than non-binaries. It can be hard for parents etc. to understand that you feel differently depending on the day.