Blank space behind transparent header on mobile, home using fullscreen scroll

Hello I apologize at first, I am new on wordpress. I am currently working on a website and I am using for the home *a transparent header *fullscreen scroll in order to go from section to section. On the computer version, everything is fine, the hearder is over my first fullscreen image in home. But on my phone version, the header is inside a white bar while the site is launching. Then when I scroll the header transparent goes at his place. I don't manage to get rid of this bar on the top of the mobile website. If I put a negative margin to the scroll section, it all shift up. So for each scroll, you have 90% of the correct image and 10% of the next one...