Jey
The first thing you need to decide is, who is going to see it.
If it will be private then you naturally have a lot more freedom to say things. But if you intend others to see it, then you will feel more self conscious.
In the latter case, it is really important to find an edge, from which to approach what you say. An essential attitude to shield yourself from some of the more nasty and critical responses you think you will get.
For example, if your journal is to be about your transgender journey.
You could start from a perspective of someone, born male, but raised as female, who now wishes to / needs to transision to male. Everyone knows you as female and sees you as such. You need to get them to see you as male without revealing you were actually born that way.
Why? The reason is, you have to have a front door, which you can shut when you need to.