It’s not completely useless in this case. You don’t say what “low SAT and ACT scores” are but 3.3 is pretty low for top 20 schools. The EC part doesn’t really kick in until you have qualifying stats. No one can say exactly what that is but looking at the Common Data Set gives you an idea. The 25% percentile for Princeton was a 32 and 75% was 35. 92% scored 30 or above. 86% had a 3.75 or above. 95% had a 3.5 or above.
Students with a 34 and 4.0 have a very small chance of acceptance like your guidance couselor stated. Please concider other options in conjunction with your guidance counselor.