Hey!
I would try not to worry that the lack of variety in experiences since university makes it look like you have given up on law. If anything, your three years of Project Management experience can be a very valuable differentiator, especially if you can articulate the transferable skills you have developed.
You already have a good foundation from your LLB (+ leadership roles, mentoring, vacation schemes, etc.), and the open days show that you have continued engaging with the profession since graduating. I wouldn't feel that you need to force yourself to accumulate lots of additional legal experiences alongside a full-time job just for the sake of having more on your CV.
I would personally focus on:
1. Making the most of your Project Management experience - highlighting things like stakeholder management, managing competing deadlines, problem-solving, commercial awareness, etc.
2. Keeping your legal knowledge/current affairs up to date - particularly in the areas of law or sectors you are interested in.
3. Being able to explain why you are interested in a career in law - why law, and how your Project Management experience has prepared you for a legal career
4. Continuing to attend the occasional open day or networking event - however, this is only where realistically possible! You don't need to turn this into another full time job
Your career history gives you something interesting to talk about - the key part is making sure that the graduate recruitment team understand why it makes you a stronger future lawyer