How to use curve fitting with log scale axis?

For the most part my graph is appearing how I wish it to, but right after the 0 time point, the graph is dipping down and I do not want that to happen, there is no data below the zero time point so I'm not sure why that is occurring. How can I get a smooth connecting line but only connecting my given data, not dipping down where there is no data?

Thanks

    % code
hold on
h1 = scatter(X,Y1);
set(h1,'MarkerEdgeColor','b','MarkerFaceColor','b');
csp = csape( X, Y1, 'periodic' );
fnplt(csp,'b');
s = errorbar(X, Y1, Z1,'.');
set(s,'Color','b');
h2 = scatter(X,Y2);
set(h2,'MarkerEdgeColor','r','MarkerFaceColor','r');
csp = csape( X, Y2, 'periodic' );
fnplt(csp,'r');
s = errorbar(X, Y2, Z2,'.');
set(s,'Color','r');
    xlim([0 96]);
    ax = gca;
ax.XTick = [0 24 48 72 96];
ylim([10000 10000000]);
ay = gca;
ay.YScale = 'log';
xlabel('Hours') % x-axis label
ylabel('CFU/mL') % y-axis label

end