How do you say "might," as in "I might be able to do that?" Is there a way to indicate that there is UNCERTAINTY here? Also it seems that native Creole speakers use "petet" differently than I would and don't necessarily understand how I use it. Any ideas?

Use ka (kapab or kab) to say might, might be able (see embedded link)
Petèt (maybe, perhaps), in Creole indicates doubt, probability, and possibility like in English.

I might be able to do that.
Mwen ka fè sa.
To add a sure uncertainty, add petèt:
Petèt mwen ka fè sa.

The auxiliary verb "ka" coupled with "petèt" should definitely get your point across:
1.
Petèt li ka fè frèt demen.
It might be cold tomorrow

2.
Li pa reponn telefòn nan.  Petèt li ka deyò.
She didn't answer the phone. She might be out.

Even without adding "petèt",  you can use "ka" on its own to indicate doubt:
3.
Mwen ka vin wè w nan mwa jen an.  M'a gade pou wè.
I might come to see you in June.  I'll see about it.

4.
Nou pa wè li depi de jou.  Li ka malad.
We have not seen him since two days.  He might be ill.

5.
Nou ka pa gen tan pou fè sa.
We may not have time to do that.

6.
Li pa't vini nan reyinyon an.  Li ka te bliye.
She didn't show up at the meeting.  She might have forgotten.

7.
Ou si se sa ou te tande?  Li ka byen te di yo lòt bagay.
You're sure that's what you heard?  She might have said something else.

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