I took a plea that the terms were 0-34 months when the PSI report came back the terms were 17-74 months what can I do?

Probation does not always get those kind of things right. Have your fiance call his lawyer.

Probation agents generally ignore the sentencing agreements contained in pleas and score based on their own assessment of sentencing guidelines. If the terms of the agreement included a particular sentencing range, the judge has to abide by this or give him an opportunity to withdraw his plea. Note, however, that it is more difficult to withdraw from a plea after sentencing, so if that request is made, it should be made prior to sentencing. These are things he will want to discuss with his attorney before he goes on the record.