Hard to tell exactly without a screencap of what you're seeing but Steps 91-103 are where you were supposed to add Email as a field in the Meeting Attendance Object. If you did those steps correctly, then when you go to Setup > Object Manager > Meeting Attendance > Fields & Relationships, then you should see Email listed as a field. If not, you need to redo those steps.

If so, then it's possible that, when you were creating the Email field, you clicked through the Next, Next & Save so quickly that those pages in between didn't get a chance to fully load & execute their logic. They turn on the Visibility of the field for all the user types (profiles). You may need to do that manually, by clicking on the Email field (after Setup > Object Manager > Meeting Attendance > Fields & Relationships) and then clicking on Set Field-Level Security. Then, under the Visibility column you need to find the row for System Administrator and click the checkbox so it is checked (and blue). Then click Save near the top.

Then you should be able to go back to Step 91 and resume the instructions.

If not, then I'm not sure so do the following 3 steps to give me access to your SF account and let me know when you've done them so I can go in and see what's going on, ok? Here they are:

1) Click on the character at the upper right corner and then, in the popup, click “Settings”

2) On the left vertical menu, click on “Grant Account Login Access”

3) On the row for The Max Labs Project, use the menu to change “—No Access—“ to “1-Month…”