I doubt the screen is “too big”. What probably happened is that the housing was dented or even bent/warped which causes the replacement screen to not sit completely flat on the housing. Check the corners of your iPad to see if that have dents and put the iPad on a flat surface to insure that it is not bent or warped. The shop may have missed this.
When I get iPads like this, I remove the dent or work the housing as flat as I can. Only once did I receive a device that was warped to the point where I couldn’t flatten it enough for the screen to sit properly.