I know, and I totally get you! Having a lot say, but restricted by the 650 word limit?
The best thing you could do is to create an essay outline (since you have selected a prompt, right?). It's up to you if you want your essay outline to contain guide questions, key words, or some lines that you want to include on the essay - whatever works best for you.
Upon creating an outline, ideate how will you craft an amazing introduction that will work for admission officers. This will be your first paragraph. I recommend creating an introduction with an anecdote, since it works best for essays. Make sure to avoid cliche introduction like famous quotes and stuff, the more you make it personal, the better. Tailor your introduction on how you will introduce your life story or success story if ever you are a speaker at a conference! How and what will you say to catch your audience's attention? How can you create an effective rapport?
Second, per paragraph, assign a topics that will complete your narrative as a whole. It could be like these:
I. Intro
a. ...
b. ...
c. ...
II. Glimpse of Childhood
a. ...
b. ...
c. ...
III. Challenges encountered as you grow up; middle school (or high school)
IV. etc...
The idea is, per paragraph, you have something to talk about (which is still relevant to your personal story. Make sure to link each paragraphs to each other to avoid confusion, and to make it coherent). Outlining will definitely help you lay out the things in your mind in an organized way, especially if you have a lot to say.
Here are other tips I can give:
1. Avoid talking about your ECs and accomplishments on the essay. let the Common App/Coalition form speak about your ECs and accomplishment. You can talk about one or two ECs, but make sure to know when it's too much. Remember, repetition of information is redundant.
2. Use anecdotes. Your accomplishments are great, and using anecdotes all throughout the essay will help the reader visualize your narrative. Use adjectives (at moderation) and analogies to help the reader come up with imageries. Remember: Show, don't tell.
3. Find the middle ground of all your potential essay topics, and link them together. Try exploring your ECs more, and how they relate to one another. I'm pretty sure you'll come up with ideas on how they are connected to one another, or how one benefits the other. Consider portraying a character that's fond of interdisciplinary approach, since it's evident that you thrive at different areas.
Lastly, which I cannot emphasize enough...
4. Keep it personal. I know you are a great student and you excel in every way. However, there are students like you out there too who could have the same ECs and awards. Do not forget that colleges do not just want students who excel in the academic field, they want students who knows how to grow and contribute outside the academe. They want to see YOU without the stressful tests and quizzes. This is your time to be warm, and show affection to things that matter to you. Talk more about life here, what makes you inspired? What keeps you going? What are your personal advocacies and how are you working to achieve them? What makes you human? You don't have to be overly cheezy, but know that personality also counts in this holistic admission.
I hope this helps!
To keep this community safe and supportive:
No worries! I also noticed some typo with my answer, sorry for that. I fixed them, and added some details again (check it out). I hope it adds additional help! Good luck!