it doesnt hurt at all. you will be fine all you have to do is relax

Anytime I've had to have anything injected in my mouth, they've always used some topical numbing agent, first, so I barely felt the needle, a tiny pinch and some pressure is really all I've ever felt.

You said that they 'don't have any gel' so I'm guessing that means they don't use the topical numbing gel. If that's the case, why don't you buy some Oragel (or another over the counter numbing gel for the mouth; the higher % of lidocaine the better) before you go in and ask them to use it?