Post Navigation and Margins

Hello everyone,
I am hoping someone will be nice enough to help me because I am so close to finishing my blog that it’s driving me crazy these last two things aren’t fixed. I have a custom theme and the designer is only responding to some of my questions and hasn’t told me how to fix the last two things. I am willing to put the CSS on here if needed or to search for where I would add things, just not sure where to look. On my blog https://caffeinatedandcreative.com I made a banner that should be extending the width of the page and basically not have a margin. I was somehow able to fix the left side, but have tried with no avail to get the right side to do the same thing.

Also on the bottom of the posts are numbers for the posts. I would like it to say next page, like my other blog https://themodernmusings.com It is the exact same theme with some different CSS. I just can’t figure out where to make the changes. I know custom theme help is normally not given, but I have gone to the designer several times and am honestly getting impatient waiting for a reply, it’s been several days. Thanks in advance.