Somewhat irrelevant to what you asked but may also help you so here goes:
Not exactly 40 (it doesn’t matter), but in my first prelims I had registered for vision abhyaas. Scored in the 60s range if I remember correctly and was very dejected. This was hardly 10 days before actual prelims. Despite this, I managed to clear the actual prelims. Since then I’ve stopped taking prelims mocks seriously except to check whether I’m making too many mistakes in static Qs.
To address your Q - please analyse the kind of mistakes you’re making. If you’re making errors in static Qs you need to revise and relearn those topics better. You can ignore random factual Qs in these mocks which more often that not pull down our marks. More than marks focus on filling the knowledge gaps. And use PYQs - they help us be in touch with the UPSC way of asking Qs and also keep the confidence high. All the best! :D