I’m nervous

So here is the situation. I’m on the nexplanon birth control. I’ve had it a little over a month. My boyfriend and I use condoms but the last time we had sex the situation was a little weird. I was giving my bf a blowjob before we put the condom on. So I was giving him a bj and was using my hand some. I’m afraid precum could have mixed with my saliva on my hand. He gave me the condom to put on him and I’m afraid the possible precum saliva mixture transferred to the condom and then got me pregnant when we started having sex. I know that my implant is supposed to be effective, but what if it’s not. Is there still a huge chance of pregnancy in situations like that? He never came while I was giving him a blow job out there is always a chance that there is sperm in precum. He waited like 20 seconds before it went in, but still