I do not know how colleges turn % grades into gpa out of 4.0, but depending on how this is done (at the course level vs overall and using what type of scale), your UW GPA could be higher than you have estimated.
How did you determine the 4.0 scale numbers - is it from your high school’s translation, or your own estimation? I have kids at two high schools; for one, 90-100% = A (4.0 uw). For the other, 90-92 = A- (3.67 uw), 93-97 = A (4.0 uw), 98-100 = A+ (4.3 uw). If your freshman GPA is essentially 3.0, sophomore and junior 4.0, that would be about 3.67 uw GPA. But, these high schools turn the % grades into letter grades prior to the grade hitting the transcript.
100% agreed he might be understating but I’m not sure the high schools change when reporting. Some may but I don’t think all. They might provide a scale.
If OP knows the schools scale for A, B, C, D - he can figure via a 4,3,2 I would not use plus or minus.
Colleges weight differently but most common seems to be to add .5 for Honors (so an A is 4.5) and +1 for AP.
Some discard 9th grade in the calc. And some discard but still review.