I don't know why I did this. they were for a science experiment.

And? What is it?
Or is it a surprise? ^^

they are just Petri dishes I made for a project. nothing special. I just wanted to make a gif

Then, i'd call this an success.
I thought, you grow something particular in it.

If you let them that way, they will either dry out over time or getting cross-contaminated.
The sealing tape has to go all around of each dish.
You can use few layers of cling film if you do not have parafilm.
Just make sure you use an untouched inner part of the roll of the cling film.
Just if you do not know already.

I mean, you didn't labeled them for no reason.

it was for a school project, but its already done, and I threw them away

Wow, cool school projects do you have.
I wish i'd had such cool projects.
One can learn a lot out of such projects.