I'm not sure what you mean by lifting up your shirt. You aren't going to do it with a fully tucked in shirt? It's legal, but sounds sloppy, and some may take it as a purposeful showing of what you normally carry concealed, not that that is illegal in itself, but that's what some might be thinking.
If it's discernible by ordinary observation, it's not concealed. This includes IWB holsters, normally.
But the more you make it look like a poorly concealed gun, the more frequently you will get into an official conversation about it.