http vs https at setup

I have just installed WordPress on my new WestHost account. When I installed it, I was given the option of selecting http or https as the default domain prefix. The installation wizard said to use https if I had SSL security (which I think I purchased as part of my WestHost account, but now I’m not sure this was a good idea).

The problem is that now I cannot view anything on the site. When I try to view the default post that WP creates upon installation, I get the following error message: “There is a problem with this website’s security certificate”. To make matters worse, I cannot now even log back into my Admin page.

I’m trying not to panic! Can anyone suggest what I’ve screwed up and how I might fix it? Thanks.