Same worries here.
My therapist and I have discussed this at length. The bottom line is that if you progress slowly, one step at a time, then there's very little danger that you'll do something you regret. Start small. Nobody's going to force you to transition overnight.
Steps you can take without any risk whatsoever are therapy (highly recommended), presentation (in private - things like growing your hair, changing the way you look and dress etc), and then low-dose HRT if you're still unsure.
By taking it slow, there really is nothing to worry about. You'll never be in a position where you look in the mirror and you're shocked to see a female face, boobs, and a vagina where you once had something else. From reading about some of the people (and it's fewer than you might think) who regretted their transition, many seem to have rushed things or "gone it alone". Don't isolate yourself, find a trusted person who can keep an eye on you and let you know honestly if you're moving too fast or if you're going to do something you might regret later.
For all the fussing about the standards of care and gatekeeping, there is some common sense behind the "barriers" that stop us from lurching ahead and trying to transition in short period of time. It's not a race, and there are legitimate reasons to have us stop once in a while and examine where we are and justify why we should continue.
And remember, once you start to transition, it's not as if you're obligated to finish. You can step off at any time, and there's plenty of opportunity to stop without anybody ever knowing if you start to feel uncomfortable.
That said, don't confuse normal worries about such a significant life change with a fear that you're making a mistake. It's normal to be slightly apprehensive about transitioning - I'd be concerned if someone didn't see any downsides or have any fears about what the future would hold. And again, therapy is a great place to determine whether you're worried you're not right for transition, or whether you're just worried about what transition entails. In other words, therapy will help you sort out whether you're worried about the reasons for transition or just the transition process itself.
You should be glad you're apprehensive. That's a good sign that you're doing the right thing!