Since your browser is "cookied" by the /magic link you registered for (aka how we track folks who register on our sites), just deleting your FUB contact won't do the trick here.
First, delete (don't trash) your own contact in FUB.
Second, clear both your cache and cookies on your browser. Here's some info on how to do that:
Third, re-connect your Slack/website integration by heading into the back end of your site and clicking "Added to Slack" again.
And lastly, whenever you're testing a page on your site in the future, use an Incognito browser window so you don't have to go through the delete/re-connect process again. That type of browser window is 'private' (aka it won't register cookies and you can test all your links that way without ever getting 'tracked').