You have to really know some one for a long time to really love them. You may be in lust. Love would be if you have known her for a year, or more and want to be with her all the time and would spend the rest of your life with her. If you really love her, she will already know, but you need to tell her as well. Support her financially, listen to her, respect her, don't cross boundaries with her unless she is 100% ok with it. Lay and talk with her for hours, be best friends, be 100% honest about yourself. Tell her your dreams for life, listen to hers.
Don't just tell her, prove it to her. Show her that you love her. Be there for her when she's upset. Text/call/talk to her first. Let her know you are there if she needs you. Send her flowers. Hold her hand. Give her your jacket if she's cold. Open her car door. Pull out the chair for her. Hold doors for her. Showing someone you love them, is a much better alternative than merely telling them.