You will affect the race in one of two ways regardless of what you do. You will either benefit Party A or Party B, those parties being the two largest parties, aka Democrats and Republicans.
When a 3rd party becomes larger than the Democratic or Republican party, you would be correct. That is not the case, so you're still incorrect.
So in your opinion what makes the GOP more deserving of your support compared to the Democrats?
Non/3rd party votes make it easier for the SMALLER party to win, and that happens to be the GOP here. This is just how FPTP voting works.
There are two possible outcomes, how could your actions not benefit one of the two possible winners?
I get that it feels icky, especially when someone views voting as a way to send a message or present their own moral views, but that's not what voting is. Not in the general election at least.