That's how I feel now, MissSMcC... I used to worry, but then I figured there is no magic clothing that will make me look slim, I look big in everything because I am. So I might as well wear what I like!!
Enjoy your style and wear what you like, this will bring confidence over worry of size.

You are your own harshest critic, I bet other people aren't thinking you look bad in the T shirt.
My only rule though is well fitting clothes- I believe this for everyone; clothes that is not too tight or too baggy look very nice, and it is most flattering too. A thing I cannot wear is tops wear you can see where my belly button is through it. I just get really embarrassed about that!!