Hello, Really cute drawing ! I think that with the angle of your bottom shadow you are missing some core shadows and some cat shadow. Also the branches should be mostly hidden in the shadow since they are in the same plan as the sun + main cactus. I hope it helps.
Thank you very much! Yes, you're right. I totally missed the other shadows, but that's okay. I wanted to have fun and the learning comes with the practice, even if I don't aim for that in this case :D
No troubles :) Have fun