When creating a table of values for the function, you may not have taken into account the negative sign in front of the term $\displaystyle-{2}{x}\usepackage{cmbright}\Huge\$ . This graph matches the function $\displaystyle{f{{\left({x}\right)}}}={2}{x}+{3}\usepackage{cmbright}\Huge\$ , not $\displaystyle{f{{\left({x}\right)}}}=-{2}{x}+{3}\usepackage{cmbright}\Huge\$ .