April 27, 2020
It sounds like you're tuned into the wrong grapevine. Colleges DO pay close attention to senior grades, especially those from the first semester. Granted, this isn't true for all candidates to all colleges, because most Early Action and Early Decision Round I verdicts are issued before first-semester grades are posted, as are many Rolling Admission verdicts. But, commonly, admission officials will ask high school counselors for first-quarter senior grades before determining admission outcomes in the fall. (And colleges scrutinize senior grades at the end of the school year and will rescind decisions … even as late as July … if these grades have plummeted since the student applied.)
While a strong 12th grade transcript won't make up entirely for a weak 11th, it can certainly help a lot, especially if your curriculum is rigorous. Admission folks do like to see what they call “the rising record," and if you can sustain improved grades throughout all of your senior year, it will definitely work in your favor if you wait until next fall or winter to submit your applications.
If it doesn't interfere with your gap-year plans, you might also consider taking a class or two at a community college or other convenient four-year school (as a non-matriculated student … meaning that you aren't enrolled in a degree program). Top grades at the college level can also help to reinforce your upward trend. BUT … tread cautiously. Some colleges put strict limits on the number of classes that a candidate can take during a gap year without having to apply as a transfer. So if you are considering taking classes during your time off, check the policies at your front-runner colleges before committing. (Note also that, even though many colleges will allow you to take classes, they may not accept your credits. So this is something else you need to check, if getting credit is among your goals.)
“The Dean" is a big fan of gap years … at least for students who are excited about taking one and who have solid plans in place. So best wishes to you as you tackle your senior classes and chart your course beyond it.