If you are asking whether you should strategically apply ED somewhere else because you think your chances would be better, I would suggest you not do that if Harvard is your top choice. I would instead make THEM say no. Or hopefully yes, but for sure they might say no. But I would not bind myself to withdraw my application just because I got accepted somewhere I would not actually prefer, without ever giving them the opportunity to tell me yes.
To the extent you are worried that you will not get admitted either to Harvard or to whatever you would have chosen as your ED school–that is an easy problem to solve because there are many, many other fish in the sea. Spend the next few months really investigating suitable colleges. Use the people here as a resource if you feel like it. There will be many great options.
Then plan to apply to a robust list of well-chosen Likelies, Targets, and Reaches. Then if Harvard remains your favorite, and you get in REA–great, done, enjoy the rest of senior year. If not, my guess is you will still end up with many good options to choose between from the remainder of your applications. Assuming you did in fact choose them well.