Did the tags state if they are on semi-dwarf or standard rootstocks? I have my semi-dwarf citrus spaced 10' x 12', that is 10 feet between trees in each row and 12 feet between rows. Six years in the ground and they are filling the space nicely. If they are on standard rootstock they will be more vigorous but you can still prune them back, at least to a point. Fully mature citrus on standard rootstock can easily fill out 20+ foot spacing.

I spaced 2 Fukushu kumquats and a Meiwa kumquat 6 feet apart outside on the south side of my house in the 6 foot wide space between my house and garage. I will be pruning mine because they are to close despite being true dwarf trees. If your trees are grafted to either Flying dragon or US897 rootstock then you chose a perfect distance for them.

6b Steve

Let's hope you have those tags, and possibly an ability to return.

do you need closely spaced trees?