Hello Georgie13, welcome to the Microsoft community, I'll be happy to help you today;
I understand that your mouse sensitivity is too fast even with low DPI;
Initially I recommend that you try the following;
Go to Mouse Settings > Additional Mouse Options > Pointer Options;
Enable the option "Improve mouse precision";
This option will slow down the mouse cursor;
Click Apply;
Check that the mouse sensitivity is now OK;
See you soon!