Problem: Resizing during export

Well, I really tried to fix this by myself but I didn`t found any answer to my problem.

I made daily Social Media Posts using Adobe Photoshop as my main software, mostly of the time, I make what we call "carousel posts for instagram"

Well, that said, I never had this problem before, which is:

- I made a new file, with the Instagram Portrait Size, 1080x1350, and then I multiply the 

width by the amount of pages of my carousel, so, If I`m making a 10 page, will be 10.800x1350 Pixels file.

Fine, I did my job and finished my project, but here comes the issue, when I slice the image using the guide lines, 
it aways made me a total of 10 imagens with 1080x1350 pixels, right?

But not now, when I try to export my project, using cmd + alt + shift + s (export for web) my document simply
started to recize for some values that I didn`t changed.

As example, this project that I`m currently working on, it`s a 10 page carousel, it suposed to be sliced in 10 files
of 1080x1350, but instead, Photoshop is setting the resolution for 819x1024, or 75,85% of the original size

And I tried in different ways to set to 100% but didn`t made it. 

Please, does anyone know what is happening here? I didn`t find any tutorial or explanation on internet

And to make it clear, I tried with different files, I tried to creat a new file, it aways happen the same thing.

Thank you for now.