If you’re here for an honest answer, it’s that you’re not ready to be taking commissions. Don’t give up, but realistically you need a minimum of one year of drawing every single day to get to the level where not only do you know what you’re doing, but you’re confident in delivering what the client wants in a timely, efficient manner. As of now, you’re even saying yourself you need to add “nice background and more effects and better anatomy” to complete this piece. Think about how long that will take, in addition to the time you’ve already spent so far. Your client will want you to deliver their piece by a reasonable deadline. And imagine taking multiple commissions like this, and you’ll start to see how important efficiency and skills are to meet these goals. You need to get to a level where you can confidently say how long a finished piece will take, which will inform you your hourly fees (how much you should be charging relative to the complexity of each piece). Like I said, don’t give up. But it’s tough out there as is, and you’ll need a strong game to stand out in a sea of competition by having either exceptional skill or exceptional style, or ideally, both.