Ok, so translation itself not so bad. Not awesome, but okay. As your first work - good.
But never EVER use left-aligned text - it will always look augly regardless of any font, effects, or whatever you could do. Always center-align it.
Also that font is too slim. Either check what other scanlators using, there are couple of famous most-used fonts in manga scanlations, but don't remember names anymore. At the very least, you can use outline to make it look more presentable.
And lastly, don't jump from one size to another too much. Choose several predetermined sets, and switch them only when necessary. If every baloon use different text size - it would be chaos.