I took a peek at your blog. As a mother myself, I am so sorry for your loss. Your blog is amazing.
So, what you want to do can be done without the custom design upgrade! It's called "Custom Menus," and all you need to do is follow the steps here:
First, you'll want to set up some pages. I see you have three set up, so that's good! If you want just those three, you're all set with this step!
Next, you'll want to navigate to Dashboard > Appearance > Menus:
I see you've already started here - but what you've done here is start THREE custom menus. You only need one. So you can delete them all and start fresh (I recommend this).
You will want to name the menu something like "Top Menu" or something else descriptive. Users won't see the menu name!
Then, you can scroll down the page and select the three pages from the pages modal on the right and click "Add to menu"
Save the menu
Then - very important - select your "Top Menu" (or whatever you ended up naming it) to the Theme Locations drop-down, and click "Save"
You should be all set!
Just let me know if you run into any issues with this!