To remove Alaska and Hawaii:
1. Use GeoVariant[Entity["Country", "UnitedStates"], "DefaultMapArea"]
as the option value for GeoRange
:
GeoRegionValuePlot[data,
GeoRange -> GeoVariant[Entity["Country", "UnitedStates"], "DefaultMapArea"]]

2. Filter data
to select the continental states:
continentalus = EntityList @ Interpreter["USStateClass"]["Continental US"];
cdata = Select[MemberQ[continentalus, #[[1]]] &]@data;
assoc = AssociationThread @@ Transpose[cdata];
GeoRegionValuePlot[assoc]

To refine colors:
1. Use the option PlotRange
to use all the color contrast for the states with confirmed cases between min
and max
:
{min, max} = {0, 50000};
GeoRegionValuePlot[assoc,
GeoRange -> GeoVariant[Entity["Country", "UnitedStates"], "DefaultMapArea"],
PlotRange -> {min, max, Automatic}]

2. Define a piece-wise color function using a list of bin limits of your choice:
binlims = {0, 2000, 5000, 10000, 15000, 25000, 50000, 200000, 1000000};
colorF = Function[x,
Piecewise[Transpose[{ColorData[{"Rainbow", {0, Length[#] - 1}}] /@
Range[0, Length[#] - 1], #}] & @
BlockMap[#[[1]] <= x < #[[2]] &, binlims, 2, 1], Black]];
Legended[GeoRegionValuePlot[Map[colorF] @ assoc,
PlotStyle -> FaceForm[Opacity[.7]]],
SwatchLegend[colorF /@ binlims, BlockMap[Row[#, " - "] &, binlims, 2, 1]]]

Aside: You can also use GeoHistogram
using state polygons as bins and Values[assoc]
as height values:
GeoHistogram[assoc, Polygon /@ Keys[assoc], Values[assoc] &,
ColorFunction -> colorF, ColorFunctionScaling -> False,
PlotLegends -> SwatchLegend[colorF /@ binlims,
BlockMap[Row[#, " - "] &, binlims, 2, 1]]]
