There are so many factors that go into a marathon training plan. Number of miles per week, what the workouts were, etc... Then there's the race itself. Fueling, pacing.
A 1:25 half suggests you can go under 3. But it'll be close. If you can handle 60 to 70 mile weeks regularly, do that. Long runs in the 20 mile range, with a 10-12 mile warmup, 6-8 mile marathon pace tempo, followed by a 2 mile cooldown - teaches your legs to run while tired. Also, do you run every day? Even if it's an easier run, training your body/mind to run on really tired legs also helps.
As far as day of race, if you felt dizzy, that can be a salt/hydration/fuel imbalance. Unless the weather was super hot or humid (which if the race was yesterday, I doubt), then you need to look at what you're taking in during the run. And I agree with the above poster about pacing. 3:00 pace is 6:52. A 2:55 pace is 6:41 and your half/10K times suggest you are not in that kind of shape.
Next marathon - make sure you are running every day, vary workouts and include the long warmup/late in the long run tempo idea, make sure you are fueling properly and practicing fueling during long runs, and be a lot more strict with your pacing. Better to run that 6:41 pace in the last 5-10K when you know you can sustain it to the finish, than at the 10 or 20K marker.
I wish you luck, good recovery, and healthy training to your next one!