Can my dentist shave down my front veneer that is a bit too long and bulky?

It would have been more ideal to have made the necessary corrections made prior to cementing.  Minor adjustments to length and shape can be made after cementation, but only to a certain extent.  If further correction become necessary, you may need to have them remade.  It is too difficult to comment on the appearance based on your photo.  Any dentist should acquire your approval on the final appearance of the veneers prior to cementing.  I would return and discuss your concerns with your doctor.  Hope that helps :)