The potential problem is if there is a form which you had to sign which says "I am a US citizen", and you signed the form (who reads the fine print, anyhow?). Unfortunately, that statement is false, and there are consequences for making a false statement. However, that law penalizes false statements with the intent to deceive, not mistaken statements. Nevertheless, this is a matter that a professional really needs to deal with. If there was no form and they didn't verbally ask you to assert that you are a citizen, then there is less of a problem (for you), but still one needs to be extremely cautious in dealing with the court.
It is highly likely that the form contained wording like "swear" or "certify" and mentions "perjury", so the error would be in the ballpark of perjury. Perjury is making "a false statement under oath or swears to the truth of a false statement previously made and the statement is required or authorized by law to be made under oath". Aggravated perjury is perjury which "is made during or in connection with an official proceeding and is material". The term "material" means "matters; is not inconsequential". The consequence of a non-citizen improperly serving on a jury is that a mistrial has occurred, which is not inconsequential. Aggravated felony is a third degree felony. The penal code says that
An individual adjudged guilty of a felony of the third degree shall be
punished by imprisonment in the Texas Department of Criminal Justice
for any term of not more than 10 years or less than 2 years.
(b) In addition to imprisonment, an individual adjudged guilty of a
felony of the third degree may be punished by a fine not to exceed
I must emphasize that an essential element is "intent to deceive and with knowledge of the statement's meaning", an element that cannot be present if there is no awareness of such a statement. Thus an innocent mistake could be legally excused. When you become aware that a statement made under oath was false (assuming such a statement was made), then in maintaining the falsehood, that would be intentional deceit. This is why it is necessary to consult with a lawyer.
On the Houston form, you would have to check the "are a US citizen" box. The Fort Bend county form has you certify and sign on the front page: it does not require you to certify that you are a US citizen, only to certify (and sign) if you are not – so if you failed to read the back side, that isn't a literally false statement. I can't locate an online form for Tarrant county, so dunno if that out is available.