it is already open ??

And

Yes CBX is open, operating 24 hours a day. By official provision, to combat the spread of COVID-19, the crossing for visitors with a B1 and B2 tourist visa to the United States is restricted. There is no crossing restriction for US citizens or residents. Passengers for the purpose of travel considered essential may also cross. For more information see https://www.dhs.gov/coronavirus/overview-dhs-response and the Official Notice of Temporary Travel Restrictions prior to your trip. Travel to Mexico is allowed. All passengers traveling southbound must fill out the health and recent travel questionnaire to show the corresponding authorities when entering Mexico.

If I just crossed it last Thursday

Give it