You're now ready to test the package. Start from scratch. If at all possible, don't install the theme back into your sandbox installation (especially if it's on your local machine). If your sandbox is all you have for some reason, I recommend you rename your existing development theme directory or back it up (so you're sure to be testing your package).
Ideally, you'll want to install your theme on a web server installation, preferably the one where the theme is going to be used (if it's a custom design for a single client) or under the circumstances you feel your theme's users are most likely to use it (for example, if you're going to post your theme for download on WordPress' theme directory, then test your theme on an installation of WordPress on a shared hosting environment that most people use).
Don't assume the ZIP or compression file you made is going to unzip or unpack properly (files have been known to get corrupted). Follow the procedure you know your client...