I'm not too quick or skilled at my job
Why don't you think you're good at your job?
I'm too slow when I'm doing work
You don't have to be the very best at your job, as long as you try your hardest. It's okay to not be as good as others, and you should just focus on yourself and not compare yourself to others as it is unhealthy.
Are you saying I shouldn't try hard if I'm slow? What if I make an effort to be better?
You should always make an effort to be better, I'm just saying that it's okay if you aren't the best worker at your job.