Looks like your 8 minute time came reasonably close to what I call normal, the curve that most closely fits ASA specifications. Since the spreadsheet shows that near 0.62, that confirms your test is sane.
As Kirk says, 4 stops more exposure would help for the 4 minute test. Next time you do a complete series, I would give 2 stops more exposure to all.
Of course it would have been better if you could see all the data in the highlights. But for darkroom printing, you only need to see what exposures gives you highlight densities around 1.00 to 1.20. You have enough information to make informed decisions about how long to develop your film.
Apart from the 4 minute test, the rest of the gradients look good.