@ FuriePhoenix: I agree with LKD and Crimsonvision; it does look like there is a bunch of extra fabric gathered into the tail to make it poof out more. I know you said you can't buy more fabric, but do you have any scraps or leftovers that might help fluff it out? If not, I would just make it as best as you can and purchase the other materials when you have the money.
Malasond: Welcome! I think an Ursula cosplay would be awesome!! I look forward to seeing you start that project!!
Secret Cosplay - 95%
Umi Ryuuzaki (Artbook Armor) - 40%
Hyrule Warriors Zelda - 40%
A-ko - Project A-ko - 90%
Rapunzel - Tangled - 60%
Charlotte Elbourne - Vampire Hunter D: Bloodlust - 40%
Minwu - Final Fantasy II - 20%
Rosa - Final Fantasy IV
Sorceress Edea - Final Fantasy VIII
Beatrix - Final Fantasy IX
Sailor Moon / Princess Serenity - Sailor Moon (Someday!!)