Why is my 't' and 'd' sound causing so much confusion for native speakers?

I’m an absolute beginner struggling to distinguish between the dental and retroflex consonants in Nepali. I feel like I'm saying 'tara' correctly, but my host family keeps correcting the aspirated vs. non-aspirated sounds. Are there specific tongue-placement drills that help with these retroflex sounds, or is it just a matter of mindless repetition until my ears adjust?