We appreciate the sensitive nature of this question. It’s challenging to confront the possibility of having made a serious halachic error.

Unfortunately, much of the halachic information circulating on the internet has not been vetted. It is important to seek out local halachic authorities and to refer only to established and reliable internet resources.

As you now realize, immersion in a bathtub does not change a woman’s niddah status. (See more here.) For this reason, you are still in niddah and were in niddah when you had relations. This is considered an unwitting transgression. Prayer and giving tzedaka are two classic acts of teshuva in this type of situation.

You should immerse at your earliest opportunity in a kosher mikveh. Be careful to follow mikveh protocols (see our checklist here) in order to ensure that your immersion is as safe as possible. As an extra precaution, because your husband is high risk, you may wish to arrange to immerse first on a given night.

Since you did complete counting a full seven clean days, there is no further obligation to count clean days or to perform bedikot.

Please let us know if we can be of further assistance.