Finding severe bugs after a release is 100 more expensive than before (2x for non-critical bugs), so how can more bugs be found before release? This article suggests combining multiple testing/review methods, particularly adding code review:

More generally, inspections are a cheaper method of finding bugs than testing; according to Basili and Selby (1987), code reading detected 80 percent more faults per hour than testing, even when testing programmers on code that contained zero comments.

So grab mgunit and write some unit/regression/system tests; get a friend and have her look over your code; have a beta test period; etc.