You should ask the seller.

Well that was helpful.

It might help if you would post a picture.

From your description, I'm wondering if you could stamp a design or rub some some paint onto those spots and add a few more to make it look like it is part of of the design. Another option would be to glue something on to cover those spots like artificial paper flowers or paper leaves. It would depend on the design of your painting.

If the seller is a reputable one, it would not hurt to approach them and explain the situation. If it's obviously a manufacturing fault they may well come to the party and replace it.

If you bought it in a hotel room as happens often in CA. where "painters" come in & paint huge canvases & you can even watch them & then they sell ones that are dry for a reasonable amount for home decor. It's understood that they are not masterpieces just something nice to fill a space on the wall.1 artist paints the same thing over & over, landscape or abstract. So they are actual acrylic or oil paint on canvas. A print can be like a printed page in a book or oil or acrylic or something like India ink which is very messy to work with. If you can't take it back then you might get a piece of canvas-small ones available at craft stores & try to match the look using various things I mentioned above. Black can be very difficult to match as many "shades of black-also gray can have several hues to it so you would have to try several things .Is the black shiny or matte that makes a difference too. Sometimes a Sharpie might work, if it's black missing. I have black t-shirt & got bleach on shoulder, black Sharpie did great job of covering it. You may need to feather out whatever you use so it's not just "round spots" that stick out. Might use small brush with something that looks like a match & see how it looks on your little sample canvas. Joanne's or Michael's has little bottles of paints & probably a matte black. Pic would give us better idea what to do. Jan