How to synthesize Boron tri-fluoride using Boron Oxide
The reaction of boron trioxide with sulfuric acid and calcium fluoride to obtain boron fluoride is given here.

$$\ce{B2O3 + 3CaF2 + 3H2SO4 -&gt;[\Delta] 2BF3 + 3CaSO4 + 3H2O}$$

Conditions 


  Boron trioxide react with calcium fluoride and sulfuric acid to produce boron trifluoride, calcium sulfate and water. Sulfuric acid - concentrated solution.


The reaction will be easy to understand if you break the reaction into two reaction. 

Babounet says:-


  $\ce{CaF2 + H2SO4}$  will give you $\ce{HF}$ so why bother if you add directly the $\ce{HF}$ instead ?


Indeed $\ce{CaF2 + H2SO4}$  will indeed yield  $\ce{HF}$ along with calcium sulfate as indicated here.

$$\ce{CaF2 + H2SO4 -&gt;[\Delta] 2HF + CaSO4}$$

This $\ce{HF}$ will now react with boron trioxide to yield boron trifluoride as indicated here.

$$\ce{B2O3 + 6HF → 2BF3 + 3H2O}$$

Thus the  products are boron trifluoride, calcium sulfate and water and not calcium bisulfate.