A fun project to play. I remember using Scratch at your age, making a primitive clone of the Pikmin games. Compared to my effort at the time, your talents on display here are impressive. I enjoyed the comedic timing of the hippo cronching down on a snack & immediately offering a comment. The comedic timing got better as the extra hippos increase in pitch for their cronch sound.
Allowing multiple seedlings in the inventory would make this game better to play. Or, a minimum effort that could be implemented in-place... Press E to open the shop. This would allow for more rapid-fire planting of seedlings without implementing the code for extra seed slots.