@panaghiotisadam: THANKS!!!!!!!!, changing the size to full solved my problem. I mean, it looks really similar to uploading images one-by-one, it's faster, and images can be seen in Carousel, wich i like. For those interested in how it looks, check it out here. I'm currently modifying some stuff, but it' will be there.
Two more questions:
1 - is there a way to reduce the margin (or the padding) between images?
2 - can i choose not to show the featured image on the gallery? i like to crop the pictures before, and i always end up with 2 images repeated.