So I managed to fix the problem, but it was a massive pain. I ended up downloading the "Dash To Panel" extension, which brought it back to full length, but it still had a bunch of issues. I ended up having to tweak the settings in the taskbar menu, and then uninstalling the Dash To Panel extension when I was finished. Thankfully this process made me realise what had initially happened.
To make a long story short, I went into my taskbar settings to look at something (unrelated to the current problem), but when I was in the "Position" tab, I didn't realise that my mouse was hovering over the "Panel Length" bar, and I inadvertently scrolled my mouse and manually shrunk the taskbar without noticing. Once I closed the taskbar settings I was completely screwed, because there was no way to get back into the taskbar settings (as far as I know), so I couldn't just go back into the settings and lengthen the panel again. Lesson learned, but this problem seriously needs to be addressed by the developers.
Through Zorin Appearance -> Interface -> Taskbar Settings.
Even with a tiny taskbar you can still press the Super, or Windows, key to launch the applications menu or activities overview (depending on your selected layout) and search for Zorin Appearance from there.
If you prefer using the terminal, run zorin-appearance — use the keyboard shortcut Ctrl+Alt+T if unable to launch the application menu. I don't think you can invoke the taskbar directly, however, since it's technically a Gnome shell extension.
Most of those suggestions weren't working for me, but one of them certainly could have. I couldn't get into the Taskbar Settings by clicking around the desktop, but I could have used that terminal script to get into Zorin Appearance if I knew that was an option. I tried multiple sources, but couldn't find an answer. I'm still relatively new to using Linux, but thankfully I was eventually able to get it to work. At least future users can use one of these steps to solve the problem.
To sum it up, as the previous user had stated, you can open up Zorin Appearance in terminal by typing the following command: zorin-appearance
At this point you can navigate to the "Interface" tab and click on the Taskbar Settings Icon. Once this is open, you will navigate to the position tab, and then resize the taskbar by extending the Panel Length.