You could use either 'left out' or 'missed out'. 'Kept out' means prevented from entering, so that doesn't work. For example, you might say that you put up a fence around your garden and it kept out stray dogs and cats. My first choice would be 'missed off', though. You leave out or miss OUT something that should be IN the sentence, but if it's something that should be at/on the end of the sentence - like a full stop - it seems more natural to say 'missed off' or 'left off'.

I would use "left out" if I was expressing this.