Is my e-commerce site secure? Https in url has a gold warning sign on it.

Please help. I asked my web developer why I don’t see https on all my website pages and they said it only needs to be in the area where people are placing sensitive information as when they place an order. Is this true. I spent $250 to buy Comodo but they can only install the icon–for some reason they cannot get it to click through.
So I went to my checkout page:

[url]https://sansabelt.com/Account/Login?ReturnUrl=%2FCheckout%2FReview[/url]
and found the following:

There is a gold triangle warning sign on top of the https that says that says the page includes “other resources that are not secure, can be viewed by others and are modifiable by a hacker.”

Is my customer credit card information secure? Is my content secure? DOes this have anything to do with the fact that Comodo was not installed properly?

I would appreciate any guidance as I do not trust them for many reasons I will not bother you all with here.
Thank you.
Lily

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