Zina or fornication (in Islamic terms, which is the subject of certain Islamic laws) means for a man’s penis to enter the vagina or anus of a woman until the glans is completely enveloped without the two being married or at least ‘similar to married’ (“similar to married” is a fiqhi term that has its own explanation).[1]

Therefore, although technically, what you have done isn't zina in Islamic terms, nevertheless, it is a sin and haram; because any lustful interaction with the opposite gender is forbidden and haram. At the same time though, Allah (swt) has vowed to forgive the sinner if he repents from his sin. It is also noteworthy to let you know that your marriage is valid.

In order to get more familiar with this subject, you can see the following:

The ways of purifying oneself of sin, Question 470 (website: 511).

Forgiveness of great sins, Question 843 (website: 914).

How to be freed from sin, Question 5189 (website: 6613).

Repenting from sin and being loved by Allah (swt), Question 3704 (website: 3955).