No--you are indeed correct. I use a 1cc slin syringe and I inject 0.1cc subQ using a 30g needle to get my 500iu dosage. For a 1000iu shot, you would inject 0.2cc.
I like the small needle because it doesn't retain much within its hub. If you use a standard 25g, 1 1/2 inch needle quite a bit stays within the needle itself, giving you less. You can obviously avoid this in 1 of 2 ways. Mix it in a larger amount of bacteriostatic water so you give yourself more total volume per shot, or buy your hcg vials in the 1500iu range.