Player slips through the tilemap collider 2D.

Hi all, I hope everyone's safe. I'm building a little space shooter to practice my 2D skills and I noticed a glitch/bug. I have the borders/walls set up with a tilemap collider 2D as shown below.

The colliders usually work but if I try for a while eventually the ship gets through the collider. This is a section of the level where the player is meant to be able to get stuck if they make the wrong choice. If they then are able to jitter throught the colliders, that eliminates the whole point. The image below shows a ship that got through the first colliders. I have googled and searched for an answer, but I haven't found anything. Is this a bug or is there a certain setting that I have to adapt? I just have the tilemap collider 2D with the default settings. I would love to know if and how I can fix this issue.

Thanks a lot in advance! Bart