I filed I-539 extension for B2 visa on April 2, 2020, but I have not received any result. I only have the 13 digits receipt. Should I leave?

An applicant for timely B-2 extension is entitled to remain in the US to await the results of the decision, but your better action if you were going to stay past the time that you earlier requested would have been to apply for another extension. If USCIS approves the extension request (six months is the maximum extension time), that will be over the time from April 2, and you will begin to accrue unlawful presence as soon as the decision is made. Whether you stay or leave at this time is your decision, but USCIS would likely prefer for you to leave if you did not file another extension request or other application to attempt to maintain your nonimmigrant status. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.