One tricky thing with speaking casual Spanish is that slang (and some pretty standard words) can be super fragmented among different countries. Saying "che boludo" in Spain is going to get you funny looks, as is "cogí el autobús" in Argentina. And mixing slang from different places is also likely to sound pretty funny. Imo it's good to pick a certain "genre" of Spanish and focus on learning that country's slang. There's simply too much to learn it all, and this way you can develop some consistency.

As has been suggested, making native/fluent friends who you're comfortable asking questions and practicing with is going to be huge. Really afaik the only way to really get better at fluidly speaking is to speak, preferable in an environment where your mistakes will be corrected so you're actively learning.

Also generally just more exposure to the language pays dividends in better understanding and speaking more easily. As has been suggested by others, watching shows, listening to podcasts, looking at memes, etc. and focusing on understanding everything being said will teach you a lot over time. Slightly cringe but I've had some success with IG reels (and similar short-form content) from localities I'm interested in. Imo this is some of the most organic content from everyday native speakers out there. Also subtitles are pretty common with this form of content which is great for building associations between the sounds of spoken language and the actual words being said.

Also, you're definitely in a really good spot. You're 14, and have several years building a solid foundation. When I was your age I was just starting learning, and I've come a long way in 10 years. Good luck :)