At the size you are purchasing the tree, the easiest way to distinguish between Acer glabrum vs. Acer grandidentatum would be the leaves or the twigs of the new growth. A photo of each is attached, and some general information below with a link to more detailed information.

Acer glabrum

Rocky Mountain Maple

Leaves are palmate with 3 lobes separated by very narrow gaps and hairless surface. Bark is thin, grayish red-brown, mostly smooth. New twigs are green, then turning to a purplish young stems, maturing to gray.

https://facilities.utah.edu/facility-operations/landscape-maintenance/tree-tour/rocky-mountain-maple...

Acer grandidentatum

Bigtooth Maple

Leaves are 3-5 palmate lobes with a few blunt-tipped teeth on the margins. Bark is thin, dark brown and develops plate-like scales when mature. New twigs are bright red-brown, graying with age.

https://facilities.utah.edu/facility-operations/landscape-maintenance/tree-tour/bigtooth-canyon-mapl...

For additional images, identification, and information, see this link: https://oregonstate.edu/dept/ldplants/1plants.htm#acer

Correctly identify which tree you purchased first. If it was indeed mislabeled, contact the nursery's owner/manager directly to determine how to best rectify the situation.