How can I tell her how I feel about her

Am a straight girl and am deeply in love with my headteacher who's lesbian. I want her to know how I feel towards her but its really hard for me to just go to her and tell her that. She's 41 n am 26 n it's been almost 3 years that my heart started to beat when I see her. Every time I see her my heart has a race n my legs weakens I get really nervous n can't get my words out properly so I tend not to speak when she's around but I do t want her to think that am blanking her. What can I do pls help thanks