It's very upsetting when this happens, especially pre-T. But to be perfectly honest with you, it actually makes more sense that this happened in a gay venue rather than in a straight venue.
You know why?
Trans guys are practically invisible in society, both pre- and post-T. Pre-T we're presumed to be lesbians, and post-T we tend to blend in like any other guy. And because lesbians are much more visible in LGBT spaces, anyone who might be perceived as female but who presents as masculine is much more likely to be seen as lesbian by other LGBT people - especially if you're there with a girlfriend. After all, lesbian couples are a familiar sight in gay spaces... but how many people can identify a pre-T trans guy on first sight?
The only places where I got uphill when I was pre-T was in the men's room in LGBT spaces. It hurts, and it's heartbreaking when it happens. I can tell you from experience that it's even more heartbreaking if you're a gay trans guy, because not only are you presumed to be a lesbian, but the guys you're attracted to treat you like you don't even exist. You feel completely invisible and excluded from their circle.
But T does magical things, and there comes a point in most of our transitions when we blend into the background and are no longer seen as being 'female'. In the meantime, I found it helpful to remember that people like those guys you encountered are merely unfamiliar with trans guys, and that this is not your fault. There will come a time when anyone who tries to call you a 'girl' will look like a complete idiot. Please don't let someone else's ignorance get you down. Hang in there until the magic happens; life does get better!
And well done for having the courage to use the men's room there. That was just one unpleasant experience, but please don't let it put you off trying again.