Reaply maybe ... dunno, have to keep researching.

But Hex is regular leveled spell ... same as Misty Step, same as Healing Word ... and yet you cant use neither of those in same turn as any other spell that isnt Cantrip. O_o
So if this rule would be aplied ...
I dare to say that you would need to separate it into two turns ... like this:
1st round: Hex + Eldrich Blast (since that is cantrip, and therefore okey)
2nd round: Scorching Ray