Have you performed the adjustments in the service manual? There are a few thumbwheels that can easily change the vector alignment.

If you need to center the image on the screen, do not adjust the DAC offset control at the rear of the CPU PCB. This advice is given frequently but the correct method is to use the yoke magnets.

I have seen some issues with text rendering that are impossible to adjust out, usually involving the topmost line, as is happening in your pic. There is something about the BIOS's rasterized text routines that the Vectrex can have a difficult time with. I have a project Vectrex that has text problems but I haven't had time for a proper investigation yet. Other than not being visually perfect, it doesn't have much bearing on game play which is nice.