Hair extensions? Quality Range HH European Weave?

So today i bought some hair extensions, the people in the shop recommended Quality Range HH European Weave, i got the 18 inch in colour 4 but when i got it home and sorthed out hol long i was going to cut them, i doubled them up like they said and i can only make around 4 strips of hair? i was thinking of buying some more exactly the same for cheaper off the internet? how many should i have really? because my hairs quite thick.