Has anyone used a pregnancy test from The DOLLAR STORE? ?

Help.. Ok so on 09/27/08 had 2 follicles size 23mm @ 22mm, I got my HCG shot on 09/27/08 the same day.since the shot which was 6 days ago, i did a pregnancy test from the ( $ store) and it was negative. i did it 2x.still negative.. wouldn't it of at least pick up the HCG from the shot i got on 9/27/08? you know like a (FALSE POSITIVE) or is it too early to test? or because there cheap? or is it really negative... :( please help!!!!