5- day course of cefprozil antibiotic for sinus infection. is this enough?

Depends: If the sinus infection responds quickly it may be enough. Sometimes sinus infections need to be treated for 2-3 weeks to resolve.

Yes: In adults with sinus infections, a 5-7 days course of antibiotics is enough. Longer use of antibiotics tends to be just as effective and may cause more side effects (and, likely, breed resistance to antibiotics too).