Why do so many girls find me attractive!? I hate it, what should I do!?

OK, I went to the gym early this morning, and I saw these college girls (I think so, anyway) over by a corner. And they kept looking at me and giggling and smiling. When i was bending over doing some stretches one of them slapped my . SO I went over there, there were five of them, and the girl who did it apologized. Then we started talking, the six of us. Like, out of the five, four were staring at me dreamily, which kind of freaked me out. I told them my life's story. I came to the U.S. from Colombia a few years ago. I told them some Spanish which they loved. They also said they loved my accent. I was like, "umm... thank you" It was getting awkward. They were telling me how good i looked. 'i can tell you come here often," One of them said feeling my biceps. "Oh, no, I don't really have muscles, I've only recently started coming here," I stammered. I have a girl that I love and I've been planning on asking her out soon, and I don't want any other girls in life. I want my love to be special--If I succeed in winning her heart she will be my first ever girlfriend, and hopefully my only one. I want to marry her someday, so she can be special to me and have some sort of story. She is Colombian just like me. So these girls were getting all flirty and I tried to pull myself away (Making excuses) but they were all holding me back, feeling my muscles (I have very small ones anyway!), stroking my chest. I don't know why they found me so attractive. I am nerd. Like I told them. I love reading and writing and doing science experiments, and I am very geeky and neat and a perfectionist and a hypochondria, but they were even more attracted to me. I told them my views on women being precious creatures who are there to make a man's life joyful,to love him, for him to do the same, and how I wish to only have one girlfriend my whole life so she'll be special and how much I will love her and how I love to cook and clean. Really? These girls finally left and now I steer clear of girls all together if they start getting flirty. So, what I want to know, is why do they think I'm so attractive? Being Colombian I have bronzed, tan skin. I have been working out and seeing great results, but nothing like they said "ooh, you are the fittest man I've ever seen!" Yeah, right! I have black hair, gray eyes, and I'm tall. DO I sound attractive to you? No. Why else would I be going to so much trouble to ask out the girl of my dreams, I want her to say yes. My younger brother (Who loves tormenting me) calls me ugly as **** every day and I've gotten used to it. He calls me nerdy and dorky and weird. I guess that's why I don't find myself attractive. But please, what can i do? I hate when all these girls throw themselves at me! Gosh, have some dignity! This isn't the fifteenth Century where a girl has to bow down to a guy. And then they are so surprised just because i reject them. Please, what can i do?!