I think the first step is to really and truly think to yourself, who do I know that I can talk to about my fears and concerns? And then tell them what you’re passing through. Someone who hopefully can be primarily someone who listens to you before telling you what to do.
From the issue at hand, it sounds like some of your anxiety and perhaps resultant depression is from the pressure you experience about trying to keep up your performance in school and underlying fears about how your parents might react if you “fail” them. In an ideal world, your parents would be the first people to talk to. If you’re closer to one than the other, talk to that one. Tell them your fears, and how they are affecting you.
In terms of generalities, keep social, keep active, eat well, don’t stay cooped up. Find moments of peace and relaxation and indulge. If it fits you, explore meditation and mindfulness. But really, those all are aids to ensure things don’t get worse, it does sound like there’s something more going on underlying that needs to be addressed.
And yes, if you’ve read all this and think it isn’t for you (or try it and feel it doesn’t work) and/or it appeals to you, seek help. Many schools, for example, have mental health professionals on staff who are there to listen to problems exactly like this.
Best of luck!