Do you mean you're at the bid, not at the ask?

If so, at half a cent lower, you're probably at the back of the line.

At the ask, that doesn't make a whole lot of sense. There is no way at all that you shouldn't be able to buy shares at the ask, if there are shares offered for sale.

Several years ago, it was still possible to do "all or none" orders. In that case, if the only orders at the asks were that type of order, and your bid was for a lower number of shares than the smallest of those orders, a bid at the ask wouldn't have been filled.

But that doesn't make any sense at all now. I've never put in an order with a limit at the ask amount and not had it go through immediately.

I bought some about a week and a half ago at the ask (2 cents) and it went through right away, and that was a moderately large order (405k).

If you're trying to buy at the ask anyway, have you tried putting in a market order instead of a limit?