Hi, Jade! Glad to hear you're enjoying Mandarin, too.
I remember when I first started learning Mandarin, I really struggled with tones (like pronouncing my third tones as second tones). Whenever I made longer sentences, I'd also fumble over the tones, too.
What ended up working well for me was to not think about individual tones. Instead, I listened to complete sentences from native speakers and copied them verbatim. In practice, this meant either listening to videos on YouTube or asking a friend who was a native speaker to record themselves saying something for me. I'd basically play the sentence over and over again and repeat it aloud, listening to the speakers rhythm and pitch. It was a bit tedious when I first started, but it REALLY helped down the road because now I rarely think about the tones.