Translation:I am going to bed at eleven o'clock.
Is it un ar ddeg or unarddeg? Only the first gets marked right here but "unarddeg" has been right in other cases...
It's not a verb but a noun, and gwely is the correct spelling according to the dictionaries I've checked.
(You may be thinking of the rule for verb endings where "e" goes with "u" as in gwenu?)