Bhavana, your name hints at the right answer.
I would assume that your home language is a North Indian one. In North Indian languages there are two sounds that sound to an English speaker like the English 't'. On the other hand, they don't have the sound of 'th' in 'thumb' or 'threat'.
One of the Indian sounds often sounds to English speakers like the 'th' in 'thumb', so much so that sometimes you see names like "Gita" and "Tara" spelled "Githa" and "Thara" in an effort to show the dental 't' of Hindi.
On the other hand, to Indian speakers, the English 't' sounds more like the other, retroflex, 't'.
So when you hear an English speaker saying 'threat', you hear the dental 't' at the beginning, and the retroflex 't' at the end. But the English speaker has used a dental spirant at the beginning - 'th' - and an apical stop 't' at the end. Neither of these occurs in any North Indian language (but apical 't' occurs in Tamil).
You feel, without quite knowing it, that you should be using a dental at the front, and a retroflex at the end. But it's quite hard for anyone to shift rapidly from the dental to the retroflex position, certainly within a single short syllable. So you produce a dental at both ends, and this is what bothers you.
Rather than fuss about it, just accept that it gives a charming sound to your English - rather like that of my wife Githa and her sister Thara, whom I can't persuade to spell their names any other way!