Hi qnkov,
Thanks for contacting us about this, I will be happy to help.
Judging by your screenshot that you kindly included, it looks like the CSS of your theme (Animestream) is causing the image to increase in size, I tested your pic on my test site and had no such issue. With that in mind, it appears to be your theme that is increasing the size of the image
I included a screenshot of the CSS causing the size change. https://ibb.co/SnsfnBr
I recommend this possible solution. If your theme allows you to add Custom CSS you can use that or you can download a custom CSS plugin of your choice.
To that custom CSS field add
.page img {
width: auto !important;
}
When I tested this CSS adjustment with your site, the image reduced to the correct size.
I hope that answers your question but if you have any more issues, feel free to reply back to this question.
All the best.