Fajr time was at 3.44am today. I was eating until 3.43am and when there was around 10secs left I intentionally swallowed the saliva at the back of my mouth which contained melted chocolate full well knowing that I may probably run out of time whilst swallowing this.
The first swallow was within time yet the second swallow that followed (didn’t really have control over it) happened when the clock hit 3.44am.
Is my fast valid?

You should give yourself time before fajr which is called imsak where you stop eating and drink prior to fajr by 10-15 minutes. In your case now you should consider your fast valid but as ihtiyat pay kafarra of feeding 60 people. This can be done anywhere as an example this would cost $30 in Afghanistan or less in Iran. Also as ihtiyat to do the qadha