Summers are always great to show you do something.
Whether it’s a job at the grocery store/McDonalds, etc. or working on a research project (not paying to do so), how do you want to spend your summer.
We sent our son to a one week STEM camp at Purdue - STEP - not to help his applications - but like you, his interest were varied but he settled on engineering - and we wanted him to have a chance to validate that it would be the right choice.
But work, volunteer in the community…walk dogs at the shelter, help in a food pantry or find some volunteer opportunities from your city…all these things are great.
You’re already doing, according to you, paid grad level research - so why not continue if you enjoy it and it’s avail…during the summer. If it’s not enough to occupy your time, the local grocery stores and fast food places will all be hiring - or find another role. Jobs show responsibility, team orientation, etc.
That said, you’re profile is already strong so I’m not sure that there’s get you over the curb thing.
You already have a chance at most every school. Reach doesn’t mean you won’t get in. Reach just means - these are very difficult schools to get into and while many do, most don’t - so it would be criminal (in my mind) to tell someone they have a great chance when a school admits 3%, or 8%, etc. of students.