Correct. Send the letter to the address indicated on your receipt notice. You are withdrawing the petition. Include both full names and dates of birth AND the case number. It is not critical that this letter is received before the petition is received. You can send at the same time, but to two different addresses. Petition goes to different address of an intake facility, not to the actual service center where your existing petition is.
Perhaps unneeded advice, but THIS TIME, become an A-Student of the forms and instructions before filing.