More literal answer this time:
LIGHT (or perhaps PHOTON).
What you see here is plainly in sight
You need light in order for your sense of sight to work.
And nothing here is made of letters
That wasn't just a letterplay clue ("in sight" meaning a letter of the word "sight").
Give it a try - what am I?
I'm everything that is not quite right
"Not quite right" could refer to the weirdness of wave-particle duality, or to the fact that the word LIGHT is not quite the word RIGHT.
Please forgive me find what matters
Tell me, quick, for sometimes I lie
"Lie" in a wave formation - or, again, wave-particle duality, light 'lying' about its very nature.