I don't know what you are using for a "reference", but if you are comparing the recorded sound to the sound "in your head" then you haven't considered the contribution of bone conduction. Put on a good sealing pair of headphones or even put your fingers in your ears and start singing, Hear all that bassy sound? That's the sound traveling through the bones in your head, and your ears pick that up and mix it with what comes in from the air. Hence what you "hear" is not the same thing as other hear from you.
You need to get accustomed to hearing the real sound of your voice,
A couple of other issues I heard were some annoying plosive sounds, which are wind blasts from your mouth to the mic. Are you using the pop filter that came with the NT1? You need that. You can also move the microphone slightly to the side, or put the capsule so that it is about level with your nose. It will still pick everything up, but any strong breathes will be directed below the capsule, so you won't hear them the popping sound.
Finally, there is quite a bit of high frequency sound, particularly with sibilant sounds, F, S, T etc., You can use a bit of EQ to lower the extreme high frequencies.
The NT1 is really a very neutral sounding microphone. It really shouldn't be sounding thin, unless the source is that way to start.