Closing off a shape

Hey y’all, I’m very new to Blender. This is my first project that I’m working on. It’s part of a Corona Virus board game. Anyways, my professor has asked me to split the virus in half in order to make 3D printing easier. What’s the best way to go about doing this? I used the bisect tool on a duplicate to show how the inside looks. The problems I’m running into are:

  1. If I use bisect tool, it gives me the option to clear the inner/outer/fill but choosing any of these options deletes the other half of the virus which then leaves me with an incomplete piece.

  2. When I bisect the object, it becomes an open shape, which I assume isn’t going to work for 3D printing.

Make sure you’re in Object Mode, then add a Solidify modifier to the model. Thickness is the main property.

There is a few ways.
Here is one way: