Customize HTML link gone?

Recently, I tried using a theme from tumblr garden. I decided that I didn't enjoy it as much as I wanted and I went back to the customize page to change it to my original HTML theme. However the link to customize my HTML wasn't there. I've tried refreshing and several other tricks but it doesn't seem like the link is appearing anywhere in the theme tab. When I open my theme tab all I get are the themes from the tumblr garden, no customize HTML link. Has this happened to anyone? Is there anyway to fix this?