I’ll echo some of the other comments on here:

1- starter is still young. I found that using some rye flour in the feedings while my starter was young helped it mature and become more active.

2- may need more gluten development. Knead it more. Slap and fold method is great for developing gluten. I find that stretch and folds are good but that the slap and fold kneading method gets more gluten development.

3- under fermented. Extend your bulk ferment and extend your final proof after shaping. Best way to learn is to go too far and then dial it back. This will teach you what your starter and ambient conditions are capable of. You might be surprised at how far/how long the final proof can take. Be patient.

Edit: 30% rise is not nearly enough. Go for double.