By "pan", I'm assuming you mean pansexual. If that's the case, then it sounds like the T is making the part of you that is attracted to men more active. There's nothing wrong with that!
I also know a number of trans women who identify as lesbians, but they are not by any means the only ones out there! Heterosexual or bi/pansexual trans women also exist, and there are plenty of them. Being more interested in men doesn't necessarily mean you're no longer interested in women; it just means, from what you're saying here, that you're more interested in guys than you used to be.
Maybe consider it a broadening of your sexuality? It sounds like you are worrying a lot more than you need to. And I mean, when you're on HRT and new stuff is happening with your body, it's really easy to worry, but try not to add more stress to yourself. Being trans all on its own and transitioning is stressful enough.
Take some calm, deep breaths and ask yourself if this is really worth the level of worry that you're giving it. *hugs offered* and *hot chocolate or soothing drink of choice offered*