As you have figured out, your challenge is your height (or lack of) as it relates to being a NCAA Division I Outside Hitter. Volleyball is a height driven positional sport; unless you are a libero or the team runs a front to back 6-2 offense with the setters.
5'8' ish is on the edge of being a DI OH, and you would want to have a good vertical jump to compete. VolleyFamilies have to remember that there is a range of DI play. Because of the influence of the power conferences, we tend to only see these elite programs on television. It is because of this visual, that we get the impression that all NCAA DI attackers are monsters with huge jumps!
When you start to look at the mid-majors, and 'no-name' DI conferences, you will begin to notice a larger number of attackers without the height to top the Christmas tree. 6' middles and 5'8" outsides can be found at these non power conference programs. With the 'shorter' player competing at these programs, they will still be athletic (jump high, very quick).
A smaller player, playing at the DI level, must be athletic and complete in their skill sets. The tall players can 'get away' with not having the best armswings, or not being disciplined in their court movements, or not being in peak physical condition - This is not the case for the smaller players.
As to your question, yes, you can play NCAA Division I volleyball as an Outside Hitter but it requires you to be very good in all the skill sets and very athletic. With your current age, as you prepare for this challenge, I suggest you focus on skills right now and not so much physical improvements. Your body is still developing (and maybe growing) and you are only a freshman, so to go into an intense physical regimen is not the best use of your time.
Instead, focus on becoming the old school, all around outside hitter by mastering all the skill sets in volleyball. The old school OH's could do everything; pass, attack, block, serve, defend, set.....there was no weaknesses in their game! The younger you learn and practice these skill sets, the more complete of an outside hitter you will become.
If you can master these skills, then when you start to get stronger as you become older, you can add a physical regimen to improve your quickness, vertical and power.
I will close with two points:
1) Smaller players must be very patient and focused in the NCAA Division I recruiting process because they tend to be later commitments. DI recruiting has become fluid; programs offer athletes early and late. At USA Volleyball Junior Championships last summer in Dallas, there were NCAA Division I programs offering full scholarships for the fall! The unsettled nature of DI with coaching changes, conference changes, early commitments that decide to transfer after a year or two, coaches cutting players who don't get better, all result in the DI recruiting process being constant.
2) As I have written about many times, both here on collegevolleyballcoach.com and Inside College Volleyball, the NCAA Division I level may not be the best choice for a player's collegiate future. I personally believe that the NCAA DII level may be the best fit for player who wants to compete at a high level, to have a life outside of volleyball and to enjoy the summer and school holidays.
Good luck and work on skills now!