There 2 schools of thought regarding this issue. Some feel that it is a safety to have just in case, and some feel having the safety net is wrong if you have no intention to do plan B. It is a personal decision and most colleges will request a deposit to hold that plan B in place, and for some that could be a nice bit of money that the school will not refund in case you do not make it there in the fall.
If you keep plan B in place I would suggest you contact the admissions office about plan B options at that college. Some colleges will work with the student. For example, they may say that they will hold your spot until 1st day of school even though you are at the AFA and refund your deposit as long as you contact them by X date.
Remember this is not only about being injured between now and I Day, but between now and completing BCT. There have been rare occassions where kids do not make it through BCT due to medical reasons beyond their control.
~ I can recall 1 twisting their knee as they got off the bus at I Day...immediate turn back that day. Another contracted Guillain Barre Syndrome @ 3 weeks in, and because they would miss the max sick days allowed for BCT was sent back in early Aug. A third went to a HS graduation party a week or two prior to reporting where they were playing volleyball, nothing competitive, just family fun hitting the ball around with the folks/cousins and friends, and broke their wrist in a fluke move. They never made it to I Day since they were going to be in a cast until Aug.
In all of the cases they had contacted their plan B school prior to going to USAFA and were able to start the fall at that school instead of having to go to the local CC. That is to me the thing about keeping plan B and being proactive. Some will say that you are taking a spot at the college from another kid that really wanted it as their plan A. I do not see it that way at all. Colleges are like the SAs, they offer more appointments/admissions than the number they expect to matriculate, thus, you did not take anyone's spot.
Congrats and good luck.