Whats is your reaction mixture ?!? Solvent, reagents, conditions ???

BF3.Et2O is a very strong Lewis acid.

After adding BF3.Et2O, usually the reaction mixture changes its color or thickens. However, you can check the progress of the reaction by checking TLC. If there is no progress, you can try changing the solvent system.

Good Luck. 

I am using dry toluene as solvent. I am doing a  Friedlander reaction, reacting a ketone with anthranilonitrile. When I added BF3Et2O, my mixture became very hard and stuck at the bottom of the flask. I slowly added BF3Et2O at room temperature, I used dry glassware and set the reaction under nitrogen.

Most of the times, BF3Et2O reactions are instantaneous. There is possibility that the product is insoluble in toluene which is a non-polar solvent.

Please try using polar solvents like anhydrous THF or Ether and at low temperature.

Good Luck