Help to fix my white spacing issues after messing around on my completed Website?

As Nick mentions he encourages us to pick the names and colors/fonts we would like for our completed website. Ater completing the how to make a website course, I was messing around with my website and some how when looking from a mobile device the font on profile page h1 is different then the fonts on all other pgs.(problem1.) but my spacing between gallery photos are fine...however, with that said when I preview my website from my windows, theres a spacing issue on the 4th spot where my gallery photo should go, I have in my css the nth-child:(4n), so I know this isnt the issue but think I messed up with some margin issues while fooling around with the css...Any step by step help and understanding what I have done would be a great deal of help! Pr.3 is resulted when I open my page up to its largest capacity fr.computer screen, the navs to my profile about contact dont move to the right far enough it makes it to the actual right side of the page and moves up 1 row...anyhelp with these things would be awesome and an explination of what I have done to cause this problem would be of great help!