In general you made a very cool game! Level up system and overall art style direction are very top notch, sound effects were great too!
I did find cannon fire rate a bit too slow to be fair, or at least would have benefitted with causing some knockback on enemies that it hits.
I would also make the harpoon as something unlockable from the start and make it that purchasing better once would increase the range etc...
And of course, look into that UI bug for Ultra Wide screens ^^
All in all keep up the great work mate!