I am designing a basic 2 layer pcb board with altium and I have a huge doubt. Basically I used polygon pour to put my ground plane on both layers but, I wanted to clean some areas around ICs and some capacitors, like shown in the figure, I did this using polygon pour cutout, however after this, the dashed lines stay in the design, is that a problem?, It seems they could cause a short circuit
No, this is not a problem. The dashed lines are simply a visual indicator of where the cutout is drawn. They will not show up in the gerbers.
They will not show up, but you can always check the Gerbers in built-in CAMtastic viewer tool (or any other free and probably better Gerber viewer).