As above check what your autofocus point is, when you hold own the button half way, the red spot that you see through the viewfinder will be where your autofocus point is, but you can change this just by pressing the button and moving the spot.
You need to make sure that your focusing on the correct part of the flower, there isn't really a right answer as everyone likes focusing on different things, so just go with what you like. I usually focus in the centre where the pollen is, as I like the detail, but I do know people who focus on leaves, because they like to bring out the detail in them! Each to their own!!
You could also try cropping the image so that there isn't so much background space!
Are you using the standard lens that came with the camera? To get better shots you may want to upgrade, but the lens you've got is a good one to get started.
Also once you get more confident try using the Av mode on the camera, this will give you more control over the image.
Also, just for a tip, there's a magazine out there specifically for canon cameras, I think its called Photo plus, but it usually has some good tips in it!