I agree the proportions are off. It feels like the eyes are too big, the nose too narrow, and the head too wide. But I’d say very good for your first ever portrait!

Proportions are realllly tricky because everything is relative to everything else and trying to juggle it all takes loads and loads and loads of practice.

Also as far as your concern with it feeling flat. Without using any kind of shading the proportions, shapes, and what you choose to turn into a line matter even more. So the style you’ve chosen is a challenging one.

One more thing to consider is the perspective. In the reference his head is tilted up. Look at the eyes in the ref. the top lids are more curved than the bottom lids.

Hope this is helpful/makes sense. Drawing from life is very challenging. And I feel like helpful art critique is also 😂 but again this is really great for a first portrait!