Telling someone that you love her is nerve-racking. If your love for her is so strong, then you should let her know. It is better than hiding those feelings then regretting later that you never said it. 
With that said, it is still a little too early to think about marriage. After you let her know how you feel about her, just take the relationship one step at a time and see how it evolves as both of you finish school. Then see what the future holds. See if your relationship has these qualities that will lay the foundation of a strong marriage: trust, loyalty, commitment, patience, and acceptance. 
If it is true love, it will endure.