Hi João
Thanks for posting in the Lucidchart Community! You can turn off the snapping function in your Page Settings. To access Page Settings click the icon labeled 'Settings' shown below:
In this menu scroll to the 'Snap to Grid' toggle. Toggle this setting to 'Off' as seen below:
This will disable snapping in your document! You can also temporarily disable snapping by holding the 'Ctrl' key (on PC) or the 'Cmd' key (on Mac) while resizing shapes. Hope this helps! Let me know if you have any further questions.