I don’t know that variety of wood you are using, but here’s what works for me if it helps, using my customary British/European Oak where the final appearance is important. Sometimes a light finger-smear of natural oil on the dowel sides may help, but nothing that will discolour the wood. I’m thinking of Linseed oil or something similar.
1 – Harder dowel-wood, preferably the same species if you want to preserve the colouring. Alternatively a contrasting variety. Slower grown wood where the growth-rings are close together is often harder than adjacent wider, faster-grown fibres from the same tree.
2 – Chisel a longer, more shallow lead-in on the dowel end to avoid abrupt compression of the fibres where they contact the tenon hole. If there’s a tendency to damage the dowel sides, try relieving a chamfer onto the top corner of the hole in the tenon where it first comes into contact with the peg. This will avoid a crease mark as you knock the dowel home.
3 – Experiment with the gap-overlap on the tenon; you need less offset with harder woods. It only needs to slightly exceed the anticipated lateral, long-grain, shrinkage on the board end beside the mortise. The end-on tenon grain in the table won’t move.
The joint doesn’t need to be too tight. The object is to allow sideways movement as the table boards expand/contract seasonally. Remember, even after flattening and sanding, the dowel end will usually stand a little proud of the board after a couple of years. Don’t forget to elongate the tenon-holes near the edges or the table top will split. The middle hole needs to be an exact fit.
Good luck