We're dealing with a gas here, so keeping the Ideal Gas Law

pV = nRT

in mind, is a good idea

Since we're not interested in the type of gas, i.e. moles (so we don't need R either)
and the volume remains constant, pV = nRT we'll end up with

p = T, also called Gay-Lussac's Law

Now, we can set up a ratio

p_inital / p_final

=

T_inital / T_final

converting T
20 °C + 273.15 = 293.15 K

1 atm / p

=

293.15 K / 303 K

p =

[(1 atm)(303 K)] / 293.15 K

p_final = 1.0336 atm


The pressure change of this gas is + 0.0336 atm