Problem with Subfolder copying domain themes and plugin folders

Hey there! So I asked a q earlier and now I’m running into another problem. Basically I’m trying to migrate my main site to site.com/blog. The problem is, when I create a subfolder in ftp, then install wordpress into the subfolder it’s all well and good except for then on my original wordpress (so site.com) wp-admin I can not access the themes or the plugins. Other things work like posting,etc. but those two I get white pages. I have no idea how to keep the subfolder from duplicating. Help? Again, I can access wp-admin and I’ve even tried fixing the permissions (they’re on 755), so I have no idea what to try next.