We understand if it's your first time spriting, we've all been there. So we're advising you to check out and try some tutorials and do some beginner spriting and update with your new creation.
In some places for some of your sprites, it's not 100% 1 pixel thick. Especially this sprite:
You can erase the unnecessary pixels that is making the sprite look bolded and looks to be having some 2x pixel outline.