Have a plan of what you are going to do (preferably a full programme) then just suck it up and do it. You have the advantage over most noobs in that you have been shown the lifts so your odds of looking entirely like a noob are lower. It's fine to be nervous and intimidated, most folk are, but thinking about it endlessly isn't going to help. If you try to mentally prepare I think you are making it a bigger deal than it really is. Decided a day (like today or tomorrow, not next month) you will do it and be strict on yourself, don't let yourself make excuses. You'll quickly realise there's nothing to be worried about, everyone was a noob at some point and most folk who lift want to see more people starting, including more women.