First of all, congratulations on finishing you first game on time for the jam!
The screen was too big for me so making it to scale to different devices would be nice, i couldn't see the options very well but i managed to play just fine (the field was uncropped).
As other pointed out, the echo mechanic is lacking a little, i also didn't feel any difference when touching it, you could also make it move/bounce after some time.
For the bugs i found:
Learning the force field
In coop mode (or any other mode that has small field i think), if you go top left or bottom left the npcs can't hit you, so when the field get smaller you can get out of bounds and become invincible, but you can't actually hurt them, you can go back to the field but you won't be able to go back outside.
Also in pvp, when i go bottom left and shoot, the ball detects a wall and collides in front of the player.
Overall the game is fun and challenging (i really liked the music), maybe a skill or items on the field would help, also having some sort of visual effect for the cooldown of the ball to know when to shoot, and animations for the characters, other minor nitpick is that sometimes the ball goes under the field (like, the images of the faces of the characters), maybe some work on the depth of the images are needed. I see that you worked really hard on the game and is a really good start for you game dev journey, i will be checking out for future updates on your games!