You want the nock fit to be loose, but you certainly don't want the arrow to be falling off the string when you need it. If you're going to use the GT nocks from now on, you should do something to make them fit. You can replace the serving with the next thicker size. You can put a wrap of very thin material such as dental floss over just the part of the serving where you nock, although I've tried this and the dental floss doesn't seem to hold up very long. You can hold the nock in boiling water for a half minute or so and squeeze the ears together, although it's hard to get a consistent fit, and some of the modern plastics don't soften very much in boiling water. Or, nocks not being very expensive, you can just buy nocks that fit.