How to smooth the NaN values in the contour plot?

Hi I have a csv file attached and I have to plot a contour plot w.r.t date time and z values. It contains some blank data which the Matlab takes as NaN. When I am plotting I am not getting a smooth curve around the NaN values as other values. Can anyone help me out?

fid=fopen('D:\NSSS_2019\INSAT_3D.csv');
for i=1
    tline=fgets(fid);
end
data=textscan(fid,'%s %s %f %f %f %f %f %f %f %f','Delimiter',',');

x=data{1,1};  y=data{1,2}; z=data{1,3};

day={};

for i=1:length(x)
    
    p=x(i); p=char(p);
    n='00:00';
%     m=y(i); m=char(m);
%     len=length(m);
%     
%     if len<5
%        n=strcat('0',m);
%     else
%        n=m; 
%     end
    
    d=strcat(p,n);
    day{i}=d;
end
    
day=day';
day1=datenum(day,'dd');


newStr = strrep(y,':','.');
time1=[];
for k=1:length(newStr)
    aa=newStr(k);
    new=str2num(char(aa));
    time1(k)=new;
end
time1=time1';
% Grid 
x0 = min(day1) ; x1 = max(day1) ;
y0 = min(time1) ; y1 = max(time1) ;
N = 1443 ;
xl = linspace(x0,x1,N) ; 
yl = linspace(y0,y1,N) ; 
[X,Y] = meshgrid(xl,yl) ;
%% do inteprolation 
P = [day1,time1] ; V = z ;
F = TriScatteredInterp(P,V) ;
F.Method = 'natural';
pq = [X(:),Y(:)] ; 
vq = F(pq) ;
Z = vq ;
Z = reshape(Z,size(X)) ;
contourf(X,Y,Z);