Good Evening, Chokiki

Anatomy -
The anatomy of this drawing is good, however orcas have a more pronounced rostrum and also have more slender heads.
The fins looks good, however the angles seem to be a tad off. Try looking at photographs of orcas in this pose and draw the pecs at the angles in the photos.
the left one seems fine, but the right pec seems to pointing the wrong way,i think it should be angled down a bit more.

Colouring -
The magic wand tool is your best friend when colouring, select your line art and then colour on a layer below and this will prevent you from going over the lines.
I like the colour you have chosen for the body of the character, however it should not run over your lineart or into the other parts of the design of the character.
If you aren't used to the magic wand tool, you could also try creating a clipping mask which will stop you from colouring outside of the lines.

You could also try adding shading/hightlighting, which will give your character more depth, and so its part of the background rather than sitting on top of the background.
This is done by using colours darker/lighter than the main body colour and marking out where the sun/light source will be hitting the character. Use the blur tool to then blend the colour and hopefully this should give a more 3-D feel to your drawings.

Background -
The colours are a good choice, but you could spend some time on putting more detail into it. Try smudging/blurring the colours together rather than just putting them over each other. This will also create more depth.
Also I'm not really sure what the thing around Chokiki's head is supposed to be, a cloud? part of the sun?
Again you need to spend a little more time on the detail to make sure the person viewing your art knows exactly what each part of the drawing is meant to be.
Try using a colour similar to that of your light source and create light beams which again gives a sense of depth and realism to the painting.

Look at other artists work, and photographs and use these for inspiration, look at tutorials and give different techniques a go, and you'll soon find something that fits your style.

Overall:
It is a good painting, its a pose you dont see very often, but more time and thought needs to go into the execution of the painting as a whole. The lines of the character are very smooth and clear, but the colouring seems rather rushed and hasn't been thought through where each of the colours goes where.
As I said shading/highlighting will give a feel of depth and 3-D to your character and make the painting more flowing.
The anatomy is good but could do with some work, but this will come with practice, so look at tutorials and give some a go.

Just try to spend that little bit of extra time, making sure you don't go over the line art and make sure there's no white spaces in the background. Both of which really dont take very long but will definitely make your drawings better and of a higher standard and then you may get more people willing to do art trades and commission you.

These are all things that will come with time so dont expect for everything to change overnight, you need to put in the hours and take your time when drawing. It doesnt matter if it takes a few hours, most of my stuff takes anywhere between 2 and 5 hours to complete. So yeah try to plan everything you want in your head, look at photos and such and it doesnt matter if it doesnt go right the first time, there is an un-do button for a reason.

With time you will see small improvements, so keep up the drawings and have fun.