Brown oval spots with grey centres on my paddy leaves, what is it?

This sounds most like leaf blast, which makes spindle or eye shaped lesions with a grey centre and brown to reddish margin, and it spreads quickly in humid cloudy weather with heavy nitrogen. Please send a clear photo of a few affected leaves to your local KVK or agriculture officer to confirm, because brown spot can look similar but gives more rounded brown spots. As steps that help right away, stop any extra urea for now, drain and re-flood to avoid standing water stress, and remove very badly hit leaves. If the officer confirms blast, common sprays use actives like tricyclazole or isoprothiolane, but follow the product label dose, the pre-harvest interval and your local KVK recommendation, and rotate modes of action so resistance does not build up. Keep watching the neck and node area near flowering, as neck blast at that stage causes the most yield loss.