If it makes you feel any better, I made the same mistake. But consistency is key. Slowly but surely you'll get those legs conditioned. I've never been a long distance person, but I've been able to slowly but surely creep my distance up.
Not that it helps with leg strength directly but I've been doing laps in the pool every other day and after two weeks I can already feel the spike in my cardio and my core strength. It's a great way to ease yourself into things while still making good progress. Also for us future Naval Aviators, the more time we spend in the water before API, the better.