You should apply to another school ED - if and only if it’s your top choice.
Since you said Harvard is by far your #1 choice, why not REA? Or you can apply RD. And heck no should you ED elsewhere !! WHY ? Bcuz you have a clear top choice that doesn’t offer ED.
What else can you do ??
Ok your ECs to me seem a bit - I don’t want to say lacking - but if you don’t get the internship, how about a part time job - grocery store, fast food, professional - whatever. Something a bit more people oriented etc. Band or sport would be great too but likely too late for that.
Good luck.