I don't know what to do.

So no matter where we go, no matter the time, no matter if my daughter has a perfect additude all day, She would lose her shit and flip the little bitch switch. We can be walking in a grocery store everything hunky-dory, but the moment she sees something she wants, she flips out! and it's not a little flip out, its full on temper tantrum dropped to the ground, screaming, crying, kicking, punching, slapping, scratching tantrum. we cut our trip short, leave to the car(which by the way looks like I'm kidnapping her do to the fact I'm darker then her) Me and my husband have had enough. we spank her, put her in time out, take away her toys.. but nothing is working. she is going on 4.

UPDATE: nothing seems to work. I've done everything. I'm just a horrible mom. no matter what I do it just gets worse. The screaming gets loader, the fits get longer.