Fitting the plotted pixels to the country border in QGIS

I have created a plot in Python 3.7 over Alaska. Firstly, the pixels covered a lot more than shown in the image (below). Now I have set the lat lon extend to fit the plot ‘better’.

1. Is there a way to optimize this, so the plot actually fits within the border of Alaska?
2. Can I do it prior to applying it in Python, hence in QGIS?

Here is the Python script

import netCDF4 as nc
import xarray as xr
from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
import cartopy
import cartopy.crs as ccrs
import cartopy.feature as cfeature

ds = nc.Dataset(path + 'test.nc')

lons = ds.variables["lon"][:]
lats = ds.variables["lat"][:]
prob = ds.variables["test"][:]

lon_0 = -140
lat_0 = 65

m = Basemap(width = 5000000, height = 3500000, resolution = 'l', projection = 'stere', lat_ts = 40, lat_0 = lat_0, lon_0 = lon_0)

lon, lat = np.meshgrid(lons, lats)
xi, yi = m(lon, lat)

# Plot Data
cs = m.pcolor(xi,yi,np.squeeze(prob))

# Add Grid Lines
m.drawparallels(np.arange(-80., 81., 10.), labels=[1,0,0,0], fontsize=10)
m.drawmeridians(np.arange(-180., 181., 10.), labels=[0,0,0,1], fontsize=10)

# Add Coastlines, States, and Country Boundaries
m.drawcoastlines()
m.drawcountries()

import geopandas
import rasterio
import rasterio.mask

shapefile = geopandas.read_file(geopandas.datasets.get_path('naturalearth_lowres'))
shapes = [feature["geometry"] for feature in shapefile]
del shapefile

with rasterio.open("tests/data/RGB.byte.tif") as src:
    out_image, out_transform = rasterio.mask.mask(src, shapes, crop=True)
    out_meta = src.meta
out_meta.update({"driver": "GTiff",
                 "height": out_image.shape[1],
                 "width": out_image.shape[2],
                 "transform": out_transform})

with rasterio.open("RGB.byte.masked.tif", "w", **out_meta) as dest:
    dest.write(out_image)