Will turn down first investment offer of my startup (I will not promote)

Been two weeks since a holding co offered $50K cash for 50% of my new startup (since january), they also offered to do all the marketing, GTM and make a bunch of intros (i'm a technical founder).

Definitely feels good to get early validation from investors, but also hesitant to give away so much equity so early. I'm NOT exactly ready for more customers (which is kind of a great spot to be in) - i'm mainly worried about delivery and doing an excellent job for my existing clients.

My plan is to stay low and just collect testimonials, keep showing success and see where it all goes.

What do yall think? am I way in over my head?

(I will not promote)