Alright, so I make a house, it looks perfectly fine, but when you try to walk through the doorway, which I made using a Negative Part, you sort of have to walk through it sideways at the right angle to get through. How would I fix this?
You may need to adjust the CollisionFidelity
setting of your union in Studio. There isn't a lot of information about how this works available, bar this brief description on the Official ROBLOX Wiki.
You can't modify that field from a script, you can only do it manually from inside Studio.
A more robust approach, so that the functionality of your house isn't compromised by changes to the underlying physical simulation of unions, would be to make the walls surrounding the door out of multiple solid parts instead of cutting out the door frame from a single wall. This way, you will have full control over what physical shapes comprise the doorway.