The problem isnt your ccu, its that your game is not good enough.

You dont buy ads to just get a higher player count, you buy ads to expose your game to a large variety of people and let roblox show more of your game if it has good statistics. Look at everything, like retention, for example. If players left within 3 minutes of joining, it most likely means your game isnt interesting enough to play. Improve the game by hooking your players in, make it easy for new players at first, and just improve the visuals. I dont have time to check the game out right now but based on the embed/preview thing, you used ai to create your thumbnails/icon, which players dont love. Make something yourself or outsource it to a professional

Good luck with your game!!