Hi Kishan,
I’m not sure, but this could be related to the same problem I was having. When I burned DVD’s of my Rendered After Effects footage, what looked Widescreen in AE turned into Full screen “stretched” on my TV.
What worked for me was going into my comp settings in After Effects. Where it said 720 x 480, I changed to 856 x 480.
Stretch your footage to fit the new comp dimensions and hopefully you’ll be good to go.
I’m not sure if this is the proper way, but it worked for me.
If you are going HD your numbers might be different but the ratio should be the same.
Hope this helps.
-Chris