[Closed] Onza Alloy 13 tooth Cassette single speed cog fitting

I purchased an Onza Alloy 13 tooth Cassette single speed cog and its the first time i have put a single cog on a cassette,the teeth on the inside of the cog seem very loose in the grooves on the cassette and it makes me think that every time i pedal the cog will be able to move and dig into the cassette over and over again,is it correct that there should be movement and when the spacers and lock ring are fitted and tightened it will hold the cog tight or should the teeth on the inside of the cog be tight fitting in the grooves on the cassette and there should be no gaps for movement.Any info would be helpfull.