In paragraph 480 of St. Thomas Aquinas' Commentary on the Epistle to the Hebrews, he explains that the way sacrifice was done in the past was to wipe out past sins. The people sinned, and then a priest offered an animal sacrifice in reparation for those sins. This verse states that by Christ's one sacrifice, past and future sins are being accounted for, thus encompassing 'all those being sanctified.' This may seem in contradiction to Catholicism, because we offer the sacrifice of the mass every day. However, Aquinas contests that this sacrifice is no different than the very one that Christ offered, re-presented in a non-bloody form.
So in summary, Christ dying on the cross was enough to perfect all those seeking sanctification, but we have to choose to participate in that sacrifice, it is not just handed out to those who turn their back on God.