I think you have already done a great job. Here are a few of my suggestions that might be helpful.
I usually animate in After Effects, so I am not sure if all these tips might apply to sprite sheets, however I believe that these principles can be applied anywhere, regardless of the software used.
1. As someone previously answered, animate the scale from small to big. I would suggest that the first frame to be at 0px scale(if possible), then gradually grow from there.
2. Keep the accents. Those are the little stars that pop-up at the end. Try coming up with new types of accents. Here is some inspiration: https://www.youtube.com/watch?v=54-_qopqIas
3. I would also consider adding proper easing to the animation. Basically, control the speed progression of the sprite sheet within the animation. In this case, I would start quickly until the 'pop' happens, afterwards I would give it a few seconds of easing out. I demonstrate what I am talking about here: http://cubic-bezier.com/#0,.98,0,.98
(This website is used for CSS but you can use the bezier curves on the left and apply this type of interpolation in any animation program. On the page, the pink cube represent the speed progression that I would use for your animation.)
4. In terms of color, I would choose a color that suggests emphasis and a call to attention. In a lot of situations that color would be red, but see if it works in your project.
Also, visit the Adobe colors website: https://color.adobe.com/create/color-wheel/
Choose a base color and set a color rule of shades or monochromatic. Choose one main color for the sprite and use use the other ones for the edges of the sprite, for the sprite itself at different stages and for the accents.
5. The shape seems fine. I think it is a good idea to use round shapes instead of sharp ones since roundness usually conveys more friendliness.
I think you did a great job! In terms of animation tutorials, the best ones to study are the the 12 Basic Principles of Animation.
Take each one and see how it pertains to your animation.
I hope this helped and I wish you all the best in your project.Let me know if you have any other questions!
Update: I am glad you found my tips helpful! I want to help you for free, I will not charge you anything :). What I think you should do is study online principles and workflows of sprite sheet animation and of animation in general. There are SO MANY resources out there. Here is a starting point: https://www.youtube.com/watch?v=U1BQofY46AQ&list=PLYEm7rMz0yoetzd3FvBK0pLy9GaYrzyTv and https://www.youtube.com/watch?v=haa7n3UGyDc&list=PL-bOh8btec4CXd2ya1NmSKpi92U_l6ZJd . Afterwards, ask any further questions here and in this way other people will find useful tips in the future and other users will be able to see and help. Win-win :)