Wow! This is spectacular for your first Oekaki! Have you used layers? If not I highly suggest it!
Here is how layers work if you don't know.
Alright your first layer that you get is normally your background layer.
Look at the box where you can view your layers there should be a + sign.
Click that 3-4 times (or as many as you need)
I use layer two for my coloring layer 3 for the sketch and layer 4 for my actual lines. <: Then layer 1 as the background.
I hope you understood what I said but other then that this is really good for your first time!