Do you two laugh together or is it all "business/school" when you are together in lab? Laughing together is an amazing ice breaker, even though you two already know each other.
If she's looking at your bulge, that's beyond the point: she is LOOKING AT YOU, period. A lot of guys don't even get a courtesy glance, so consider yourself lucky. If you're worried about social contact, and a girl is staring at you in several different ways, talking to her honestly about anything at all, regardless of how "shy" you may come off, is going to be attention that she was hoping for.
You obviously have a lot going on. Strange all these previous encounters with girls all wind up exactly the same way. What is an example of anything you have said to them, like this incident when you were in your early 20s? Did you brag about your financial well-being, or your hot toned body, or anything like that? If you come off as overly cool and comfortable it will sound forced and rehearsed. Just be yourself. Maybe even a bit goofy.
You are in a college class together. There is nothing wrong with being a bit awkward and talking about who the fuck cares, she isn't likely hoping you land those mythical "20 right words" that signals to her "yes, the casanova I've always dreamed of" or "oh my god, what a line, I'm totally into him now" or something like that. Girls just want connection and conversation, and sexy times can follow because the comfort level can increase exponentially once a lot of talking is going on.
Lastly I didn't have sex until I was 22, and I felt just horrible for it. I mean I would just feel like the biggest loser ever about it. All through high school girls were all over me flirting and wanting me to take them out on dates, hotties too, but I never felt like I was good looking enough or cool enough or mature enough. WTF I was their same age, how can I be MORE MATURE than someone my exact same age??? So no sex in high school. College OMG girls talked to me left and right, lots of attention, lots of looks, etc. but I was completely down on myself and never went for any of it because I didn't believe I had "the right stuff." They weren't even like the hottest girls around either but they were cool. I never made a move on any of them, even talked about hanging out sometime out of class or whatever school related, but never did it. Finally after an overseas trip and the biggest chance to hook up in my life with the hottest girl I've ever imagined completely bombed because my inner self said "you can't do it man, don't think you're gonna grow up now!!" and I lost that one.
After that I was resolved: the next girl that takes interest in me, no matter what she's like or looks like, I'm going to be forward and try to go on a date. That girl was also looking for the same thing, she had been not thinking she could make it happen either and had a few sucky dates or week or two of a "relationship" but those dudes just wanted to fuck and not talk or hang out etc. We met at my work, and started to talk because we had to work together, but we started to have fun and joke and enjoy our company. Went to lunch on break several times, more talk, and finally her time was done and I said on her last day (it was a semester's time, so about 3 months...the same length of time you are in class for you) "I'd like to hang out with you after you're outta here, wanna see a movie sometime soon?" She said yes and the rest is history: we've been married for 13 years. Both virgins, some heavy petting and playing/kissing in our pasts with less than 3 people each, but as soon as we started fucking it was just meant to be. We never knew where any of it was going and we didn't give a fuck, all we knew was that we had lots of fun together, had even more fun learning about each other, and had the time of our lives learning how to have sex together. And we did it all. the. time and still do
Please just go for it. Don't be so hung up in your mind. You have a beautiful cock and great body and there can't be anything physical you are worried about. Look for a friend, they will be your greatest lover of all time.
