if i'm understanding the situation correctly (and i may not), you've managed to assemble the stem/headset correctly and are left with a gap between the top of the stem and the cap, such that the steerer tube is exposed.

spacers above the stem and the stem cap itself are essentially assembly tools. IME, a stem can be fitted correctly without their use. OTOH, if you are inexperienced installing a stem and adjusting a headset without the use of a stem cap and the proper length of spacer(s), if needed, above the stem, it might be a good idea to double check that the stem/headset is adjusted correctly.

so, as stated, if correctly adjusted, you don't really need anything more. in fact, you don't need the cap either. but stem spacers are readily available online. aluminum or carbon. google "headset spacer".