You can still test indoors and see if the mount is pointing in the general area of the object. For example you can point to stars that are at azimuth 90 and 270, and see that the mount is actually at 90 degrees to the north/south axis. Similarly, you can point to a start that is 45 degrees in altitude and see that the mount is roughly pointing that way.
The more testing you do inside, the less surprises you get under the stars.
The above tests would rule out certain errors like: wrong inputs in the spreadsheet, microsteps is half what it should, or steps per degree is double what it should, and so on ...
The "start Tracking, then slew to a star" is only a rough start. Once you are confident that the mount is pointing in the right general area, you should follow what Rafael said and do a 3 star align, centering and syncing each one. Gotos become accurate after you do that.
Another thing to check is what is our overhead limit? You can set that on