How many orbitals are completely filled in an atom whose electron configuration is 1s^2 2s^2 2p^6 3s^1? im not sure if it is 3 or 5

The number of orbitals that are completely full is 5.

The reason you may have thought it was 3 is because you're confusing orbitals with subshells.

In this electron configuration, the sub shells are:  1s^2, 2s^2, 2p^6, 3s^1

So, we have four sub shells.

Each sub shell consists of a specific number of orbitals. s subshells have one orbital, p subshells have three orbitals, d subshells have five orbitals, and f subshells have seven orbitals. Knowing this, we can look back at the electron configuration we were given and determine how many orbitals are filled.

1s^2 has one orbital, 2s^2 has one orbital, 2p^6 has three orbitals, and 3s^1 has one orbital. The first three subshells are completely full, so a total of five orbitals are full.