Thanks for the feedback.
I was aware of the scoring problem, but sadly neglected it, because I played the game so much, and new all the plants by heart, so I was able to consistently get scores of over 5.5k, without losing points by having plants die. I'll probably keep updating the game and trying out better scoring systems, but I'll definitely wait until the jam is over.
The plant with the uneven spacing was made this way, because the space I had for the next plant to be displayed was too small to display a full sized 5x5 area, and when I downscaled the sprite of the plant, it looked awful. I was playing around with it for a while, but eventually settled on this one. Maybe I'll change it again later on, when I rework the score system and the UI in general.