Stop looking at this from a negative point of view. The postitive point of view is you went and sat where you wanted and got past that step. Don't take this personally, girls just focus on what is more interesting at the time, they were chatting about stuff and unless you had something more interesting to offer they'll just focus on there chat. It's nothing to do with you at all, it doesn't mean anything about you so stop adding meaning to it and taking it as a confidence knock.

Next time you need to initiate a conversation not just expect them to start one. Who is leading here?

Finally if you've known em for a few months it may be difficult to push this anywhere if you haven't done so from the begining.

But not impossible

Of course but its gonna take some level of confidence and effort to shift this. If stiking up the conversation is a sticking point then perhaps its time to practice on some new girls?

Why didnt you just join in their conversation ?. Given the work situation and the fact that youve known these girls for some time, and your lack of experience and confidence its unlikely that youl be able to "bag" these girls so I would just take take every opportunity you can to talk to them just as practice being comfortable talking to girls.