Did you level the damera side-to-side?
One of the levers on your tripod head should allow movement on this axis.
Bubble levels come in all different accuracies and resolutions. It's possible yours is not well-suited to the task.
BTW, levels are self-calibrating.
Find a flat surface like a counter top (need not be perfectly level), and tape a shoebox onto it.
Put your level in one corner of the shoebox, up against the side, and note the reading.
Turn the level around 180° and repeat. Compare the two readings.
They should be identical. If they're not, the level is inaccurate.
The previous comments about the ground glass are important.
The GG is the final arbiter of what will be on the film, regardless of what your levels say.
Use a level that measures on two planes, and put the vertical one against the GG. Adjust the back so the GG is vertical.
That still does not evaluate camera tilt side-to-side, as discussed above. Adjust the camera as needed.
If necessary, adjust the camera tilt so the building vertical lines up with grid on the GG.