No you would get 2 1st level spell casting slots
So lets say you are a 5th level Warlock/1st level Sorcerer
You would get [2] 3rd level spell slots from Warlock and [2] 1st level spell slots from Sorcerer(or any other primary spell casting class). As you go up check the Chart on Page 165 PHB for spell casting multi class equal to your sorcerer level(because Sorcerer is your only spell casting class) to determine your new spell slot totals.
If you wanted to you could cast your Pact Magic to cast a 3rd level Magic Missile(from your sorcerer prepared spells) and attack with 5 magic missiles or you could use your spell casting and cast a 1st level Magic Missile for 3 missiles, it's up to you.
The other way around, you could use a 1st level Sorcerer slot to cast your Hex Warlock Spell. Or you could use your Pact Magic to cast the Hex spell at 3rd level(I think you get a longer duration at higher levels).