I am the worst mother ever

I'm not sure exactly where I went wrong, or how, but everyone keeps telling me that I need to either A.) be tougher on Grace, B.) teach her to play by herself or C.) that she's too spoiled. 

I don't know how I can be tougher on her. I take away privileges (like games, toys, ect), I do time outs and I've even spanked her a few times. And how can I teach her to play by herself more? She plays by herself a lot. I think that's part of the problem. When she does have someone interact with her she goes nuts.  Like her uncle, he never tells her no and gives in to her all the time, so of course she's going to search him out all the time. He's awesome with her but he needs to say no more often. 

But of course it is my fault. She's my daughter. I took the easy way out when it came to parenting. I can blame cancer and chemo all I want, I can blame my exhaustion, or my absence, but the truth is I was lazy.  And weak. I didn't put her in the crib to cry it out, I just let her sleep with me. It was easier, her crib was in my room (I had no where else to put it), it gave me a more restful sleep because she wasn't crying all the time at night. We all got more sleep. 

I mean seriously, I fucked up so badly with this kid, why should I be given a second chance? Everyone always has something to say, so maybe it's true, maybe I'm doing something wrong. 

She says long goodbyes, likes to wave out the window, tell us over and over again she loves us and will miss us. She has a hard time settling down at night without us in the room with her. That's probably because I took the easy way out and had always stayed with her until she was asleep. 

So if I'm always being told I need to fix something, and how to do it, how am I to ever feel like a competent parent? It's no wonder I feel like I'm such an awful mother, and don't deserve another child.