anyone know about twins!?!!!!? MAJOR HELP plz look and reply to

I am CD32. Did a FRER test today and came back with TEST line darker than CONTROL line.   I had a scan yesterday and saw 1 gestational sac. 
My mum has Fraternal twins so I'm super scared I'm having them. Although they grow in 2 separate sacs. Identical twins don't run in family's so don't think it's indenticals. 
•••••But although I ONLY SAW ONE gestational sac, could I still be having fraternal twins with this test or have I just got high levels. 
•supposedly ovulated 25th Dec. Making me 4W3D. Will find out 24thJAN on next scan :-). 
Thanks guys. 
•3rd pregnancy, 2nd child ✨

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