Would lifting moderate weights make my butt flat?

Simply put, I will never have a Kim Kardashian butt because I'm just not built that way.  I'm not straight-up-and-down, but I'm not super-curvy either (for one, I have narrow hips and shoulders, and that's just my bone structure).  In addition, I weigh a lot less than those models with the huge behinds.  I'd love their butts, but I like being thin too.  Can't pick and choose.

Anyway, I'm fine having a small but round behind (which is all i can hope for, really--I won't get it past 36" no matter what I do).  But in order to mold it, I've been lifting very heavy weights on the squat machine, and hip thrusts with 80 lb.  I remember back in college i did squats/lunges with 10 lb weights, and honestly I'm not sure the difference is that big.  My butt isn't THAT much bigger now than it used to be.  At the best, I've gained an inch.  Not sure it's worth it.

My trainer said I should not be lifting such heavy weights because they are bad for my back and I will regret it later.  I notice that when I do lunges with 25 lb in each hand, I get a serious burn the next day, but I just want to make sure that's a "muscle enlarging" burn, and not a "butt is being deflated and flattened" burn.  Know what I mean?  Has anyone else here built a nice, rounded, larger butt and what were your secrets?

 

Disclaimer: And just in case anyone gets pissed, I'm not trying to brag about being skinny- truth be told, I am not a fan of my body type, but I am going into body acceptance therapy and learning not to bash myself, which I am prone to doing.  I would much prefer to look like Kim Kardashian, but it's not how I'm meant to look.  Also, please refrain from useless comments like "I am super skinny but I have a ghetto booty, no offense" with no actual advice, and then no pictures in your profile that prove this.

My butt is actually kind of a flat butt. I've always thought I was built like a guy too! Narrow and not curvy! But it seems the heavier the weights when I squat the more gains I see with my booty! It has lifted itself a lot. And i squat with no less then 20 lbs. I think if ur feeling that burn, then that's good! Your muscles won't flatten out when u lift heavy! They perk up and round out! Good luck!

My butt is actually kind of a flat butt. I've always thought I was built like a guy too! Narrow and not curvy! But it seems the heavier the weights when I squat the more gains I see with my booty! It has lifted itself a lot. And i squat with no less then 20 lbs. I think if ur feeling that burn, then that's good! Your muscles won't flatten out when u lift heavy! They perk up and round out! Good luck!