I say go back through the entire process exactly as u did it. Make sure all bolts are secure and nothing was bent or is not sitt flush. Also, if it is rusted around the connection. I would recommend going to auto part store they have so many different products to get bolts off that are rusty. If u do that make sure to get a new gasket to replace on the exhaust from HD shop.
This is what I would do but just my .02. Best of luck