How do you distinguish between retroflex 'ḍ' and 'ḍh' when speaking fast?

I record myself reading Hindi news snippets daily, but I’m struggling to get that distinct 'tap' of the tongue on the roof of the mouth for the retroflex sounds. Every time I say 'bada' or 'padhai', native speakers say I sound like I’m using English 'd' sounds. Are there any specific tongue-twisters or physical cues to help me stop defaulting to the dental sounds?