Vanishing twin

I had my first ultrasound at 12+2 and was told I had suffered from vanishing twin syndrome..I feel terrible because one of my blessings didn’t make it but I’m also scared for my second baby and praying that i can carry to term...so far it’s looking good with a heart rate of 166...also this is probably the wrong group to ask this but based on the nub theory what am I having?