I hope you do realize that a quick release skewer is NOT a wingnut. You do not tighten it by just rotating the "flag" until it's snug. Have an experienced rider watch your tightening technique to be sure you are doing it correctly. This is even more important if your bike has quick release hubs too. A loose seatpost is a nuisance. A loose wheel can be disastrous.
As noted, seatposts and saddles are sold separately and seatposts come in a wide variety of diameters and the diameter must be correct for your bike. "Close" isn't adequate.