Don't panic if you have disagreements before you get married. The important thing is to learn how to address these issues as they come up. That's a skill that will take you to your 25th anniversary and beyond.
Most couples are unhappy for an average of 6 years before deciding to try therapy together. Whatever the reason (stigma associated with counseling, not wanting to admit they are "that couple," prioritizing work over their relationship, etc.), by the time they decide to try therapy, they aren't sure what happens next. Here's a little of what you can expect: