My orthodontist said my teeth can’t get any more straight than this. Is this true ? (photo)

Straight teeth is only part of what makes a great overall orthodontic result (what most people describe as a great smile).  A great smile involves how your teeth are positioned related to the rest of your facial structures, how the upper and lower relate to each other, and the angle or "slant" of your teeth.  Neither your question or arrows are very specific as to what your exact concerns are.  If you don't like your smile, be specific with your orthodontist about what you don't like and what could be done about it.  As for the straightness, they look very straight.  The bite looks good as well.  Additional improvement of the position of the teeth would require extractions.  That usually gets discussed at some point during treatment.