After arranging, there is a whole separate stage of music production (or post production) called music mixing and mastering. Basically you'll pull in a bunch of mastering plugins like EQ's, compressors and so-on until it sounds good in as many situations as possible. You'll listen to it on headphones, adjust and repeat the process. Then other headphones or speakers or as many other environments as possible (including going back to the original speakers or headphones) until you are satisfied.
Basically each output device has different qualities and a frequency response curve that you'd need to adjust for before a professional song is considered done. Many people start with studio monitors or a good set of speakers with a neutral frequency response, then move to other devices their audience is likely to listen on. Just youe speakers and headphones are good enough to start out!
I'm a total beginner myself but I bet there are some great resources out there.
Maybe something like this? https://www.coursera.org/learn/music-production-capstone#syllabus (note: all coursera courses are free if you don't want a certificate. You just need to hunt for the audit link)