It sounds like your beer will be about half as bitter as intended.
You might try a hop tea, boiling the hops in 1-4 quarts of water for an hour and straining them out, then adding the water to the fermenter after cooling. This shouldn't affect your ABV or overall flavor too badly and would probably be the best way to increase your IBUs.
Or, wait for some of the more experienced folks around here, I've only been in homebrew about a year
