The biggest thing here is the fact that you don't do the strength training in swim. I was like you, I did all three sports year round, but we had a dedicated dry-land regimen. This tended to tone me up a bit more to be strong physically and aerobically for the track season. However, I do have to agree that you won't see the same potential curve that you would if you focused exclusively on running. Admittedly, I've seen this difference more in college where the coaching is far different in the winter period compared to most of who went self-coached during the winter period, especially those without an indoor season.
If it helps, my senior year of high school, I joined the swim team and took those practices relatively hard. I would really focus on getting an aerobic effort out of the swims, and a pysical effort out of the dry-land regimen. I also chose to run to my swim practice (we swam at an external pool), and this added 4-6 miles daily to and from swim practice. So I was doing about 25 miles a week (not extremely quality of course) in addition to a swim and strength regimen.
If your swim program doesn't have its own dry land regimen, I would say that you should go for swim and some quality running. Do somewhere between 4 and 7 miles a day, with a 10 mile long run, and run at least 6 days out of the week. This, coupled with swim, will get you pretty fit for track season even without actual running workouts. It'll be a bit more difficult to run workouts because your legs won't be used to going fast, but your ability to increase mileage and general aerobic strength will be far greater than if you had just done swim.
I'd have to also agree with everyone else. You don't have groundbreaking times, you could puruse a D2 or D3 career though with your current times and probably with whatever you could run this upcoming season. Good luck!