Don't worry about not being able to have fluent/near-fluent conversations yet. Your Spanish will improve if you make consistent efforts, and there are lots of fun ways to do so!
Since you're at GCSE level, beginners' podcasts may be more suited to you. New in Slow Spanish may have a good one for you to follow along with in your free time. I also recommend Radio Ambulante.
Netflix has a fair few Spanish films/series that you can watch with English subtitles on. This will help to train your ear gradually. If you don't have Netflix, or aren't a fan of films, you can scour YouTube and find a Spanish-speaking channel that focuses on a topic you already have an interest in. Combining your own interests and the language you're learning is one of the best things you can do, as you're more likely to engage with the material. If you're passionate about music, listen to some Spanish songs. There are plenty of playlists available on Spotify and other platforms.
For reading, El Mundo news articles are something I read all throughout A-Levels. Pick one that looks to be of interest to you and take note of any unfamiliar vocabulary, structures, or idiomatic phrases. You can use WordReference to translate these (most reliable, in my opinion). Building a vocabulary bank is a good way to learn any language. You can put these words into Quizlet sets and go over them often. You can also find some short stories to read, even children's stories in Spanish. Again, if you see a particular word/phrase cropping up, make note of it and find out what it means.
For tenses, I'd suggest you find out what examination board your sixth form will be using (if not known already) and search the internet to see if they have released an A-Level textbook/grammar and translation workbook. This will be best suited to the papers you will be doing later down the line. AQA certainly have them available and I found them very useful. Do the exercises regularly and if you're a fan of Quizlet/regular flashcards, create sets with the different conjugation endings and test yourself often. There are also many websites online with exercises you can do based on your ability. Lawless Spanish is a good one.
Buena suerte. (Translation: good luck)