I think it's really a judgement call on your part. How big is the bud? A main top, or a smaller less significant flower?
Some growers remove lower, airy buds during flower in an attempt to divert the plant's energy to the bigger buds. Others (like me) aren't totally on-board with butchering a healthy plant, and tend to only remove fan leaves blocking light to some of the flowers. There is no rule that says you can't remove buds from a flowering plant, but some might argue that it could stress the plant. I say if it's really bothering you, chop it.
Personally, I wouldn't chop the bud in question. I would leave it, trying to 'steer' it along the top of the grow box towards as much light as possible, and try to move it a little every couple days to allow air to circulate around the bud (to prevent excessive moisture build-up). The unfortunate truth is that this (like most slight growing errors) can be chalked down to a learning experience. You'll know the size restrictions of your grow box better now than before you started your grow. You'll know how much the strain you're growing stretches during flower, and you'll know not to let it veg for quite so long next time.
I, too, have had a plant outgrow my box. Some buds were getting scorched by the bulbs by the end of the grow because they were touching, and there wasn't anything I could do about it, apart from wait for harvest time, chop it, and start again.
Let us know what you decide. Also, post a pic so we can see the culprit.
Peace
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