Yes...there are two ways to resign. One is a qualified resignation. The other is unqualified.
A qualified resignation is one where the least favorable characterization would be "general, under honorable conditions:
An unqualified resignation can be characterized can be characterized with "other than honorable" (OTH)
Sounds like you may have submitted an unqualified resignation.
But lets back up...
If you were under investigation at the time of the request to resign, the military would have, in most all cases, required an unqualified request. This is particularly true if you were pending charges.
This is process is often referred to as "separation
in lieu of trial" or SILT.
So if you did a SILT request? The request would be unqualified.
If you were not facing investigation or charges? Then your resignation should have been qualified.
IF that was the case, you should NOT have received an OTH...and if that was the case you can apply to have your record corrected.
But if you applied for a SILT, there is no way now to change the record.