Hey feral!
I like the lighting control and blending, and your choice of border is nice and subtle. Your render placement is spot-on, and I think that's something most people struggle with grasping early on! Kudos!
There is too much empty space on the left side - I would maybe place the text there to help fill it a bit more. If it doesn't look good, then I'd either change how the text looks or think of something else to add on the left. Another thing I could point out, and maybe its just my eyes being tired, but the render looks a bit blurry and low-res, which is unfortunate because it is a cute picture. This is made worse by the sharp background which just makes the flaw in the render stand out. You usually want the background, and other distant objects, to be blurrier than the focal point. To remedy this, you could make the signature smaller which would make the whole thing look slightly sharper, maybe a mild sharpen filter on the girl, and a faint blur to the background. You could also try to upscale the render before working on it; there is plenty of websites that will do that for you for free.
I hope this helps c: