You clear long and lat, then immediately try to use them. This is your error. You also rely on Poofing variables into your workspace... This is a very bad habit you should break while the debugging is easy!
lat = [80 45 52; 45 46 34];
long = [123 132 123; 120 122 119];
temp = [67 68 69; 71 72 73];
axesm('mercator','MapLatLimit',[-50 90],'MapLonLimit',[0 250])
framem on; gridm on;
X = load('coast'); % No variable Poofing!!
mlabel on;
plabel on;
plotm(X.lat,X.long,'k')
contourfm(long,lat,temp)
