PLS HEEELP1!! I need advice for Medibang☆ ⋆｡

Hi!!, I am in the process of creating a Webtoon comic using Medibang. But I have noticed that my lines are not polished and it looks quite pixelated, here is an example:

https://files.catbox.moe/yqwvye.png

https://files.catbox.moe/yqwvye.png

My canvas is 900 x 3280 and 650 dpi, I used this size because it is the standard for a comic(?). Should I enlarge the canvas or set something else? I hope someone can help me, but if you have tips for Webtoon it would help me. 

(btw, have a nice day! sorry if there is a grammatical error, I'm still learning english).

(I've edited this blog to try to make the image look good and not just the imgur link, I'm new here lol.In the end I used catbox because I didn't know how to use Imgur properly, sorry for the inconvenience.).