You can try using a different dye, Memento dye shouldn’t bleed, that is the ink that we use and recommend.
If you are using dye ink, you could try a different type of card or paper or a thicker card – we use Bee Paper and this works well with Memento . The pens are designed so that you do not have to keep going over the same area as you get the color gradation with the first layer of color, this should also help as you are not saturating the paper.
You could also think about putting some paper underneath to absorb excess ink. We also suggest pressing lightly on the paper so that the ink does not flood an area.