You typically need at least 2" clearance to be comfortable, without seeing you on the bike though its hard to say either way. 5'10 will TYPICALLY be a 17/18" frame, though, but is based on inseam and reach.
If its only been a few days and its in new condition (no wear) wipe it down with Pledge and take it back... they should have known it was the wrong size for you to begin with.