My dentist doesn't do numbing gel, he does acupressure, and I swear the first time he did it I thought he was some kind of magician/wizard! He's wonderful. If you can find a dentist that does that, I'd recommend it!
Otherwise, previous posters are right. The hardest part is the needle, and a lot of that is psychological. I fully acknowledge that it's scary to have a big needle coming towards you! But if you close your eyes and hold someone's hand - usually there's a dental nurse or assistant who is trained for exactly that!! - it's over in a few moments, and the rest is just oddness and weird sensations. You might have a bit of aching when the anesthetic wears off, but that's completely normal and will pass.
The biggest advice I can give you, apart from what a PP said about getting it done sooner rather than later (which is so true), is not to let it get so big in your head that you freak yourself out. In terms of dentistry, it's very minor, though I respect it can loom over you and feel much bigger if you're not used to it.
Talk to your dentist, too. It's in his best interests to make you as comfortable as possible, otherwise the procedure is that much more difficult for him to perform! And if he doesn't listen to you and take your concerns and fears into account, then find a different dentist (if at all possible). My dentist and I have an agreement that he does not move the chair once I'm in it, because I have issues with that kind of motion. But that came about because I talked to him about my concerns, and he listened.
Best of luck, OP! Deep breaths. You will be just fine. We believe in you!