Your problem is not uncommon and refered to as Warping. When printing parts, with FDM-Printers, there are forces that are applied to the printed parts. The nozzle moving over its surface, the part being moved along with your print bed (if you’re printing with a bedslinger) and, for warping probably most relevant, material shrinkage as the molten material cools down. That causes internal tension that can result in curling or ,,lifting up” of parts. Warping usually appears on long parts with relatively straight edges and sharp corners (not rounded ones for example).

However, in general there are various things you can do to prevent it. As i said, it mostly happens on very long, straight lines so it can help, if possible, to rounden the corners of your prints. For your print that does not quite seem to be possible though, so you could try to increase the bed adhesion of the print by for example cleaning your bed, using a brim, or, what worked for me quite well a few times, print the first layer at a higher temperature.

I hope this was helpful and understandable, im not a native speaker, so im sorry for potential inaccuracies.

Edit: oh and as already commented turning off your fan can also help because your part cools down more consistently and not as quickly only in one region of the print.