Why is the FBI still holding my expunged record? Texas(kinda)

Hi, so long story short when i was 18 i was arrested for felony possession of a controlled substance in Harris county Texas. The charges were later lowered to a class A misdemeanor and then fully dropped by the DA. About 4 or 5 months ago i was finally able to get my record expunged with help from my lawyer. However recently i applied to join the Coast guard Auxiliary and got a call from the person conducting my background check at the head Auxiliary office that my arrest had shown up in their system and they wanted me to send proof that i did indeed have my record expunged which i then sent. But why does the FBI (thats who does these background checks) still have that arrest on their records? I had to send finger prints and my social security number for the check. This is bullshit, i wanted to work in government (i am a POLI SCI major in university right now) when i got older but apparently that arrest THAT I WAS NEVER CONVICTED OF might stand in the way. I am honestly really pissed about this, especially sense the drugs i was arrested for were not mine (hence why the DA dropped the charge) Is there anything i can do to get the FBI to expunge this record? I know the NSA will keep any and all info till the end of time, but i REALLY don't want the FBI to keep this on their records. I think they do it through a national criminal database so apparently im still on that. Thank you for any and all tips, ill try to respond. And i tried calling my lawyer a couple mins ago and will keep trying. I am 20 years old btw