Hi,
assuming you're in a reasonable parking orbit and have ~34% fuel left in the second stage of the DeltaII, you should have enough dV for the job.
A couple of suggestions for getting a more accurate injection burn from IMFD5.1m (latest version I think)
1. Go to the IMFD "Configuration" page and increase the parameter
"AB Throttle down" from 20.0 to 200.0
2. Open up IMFD "Map" display in another MFD and watch your PeA at Mars. Kill the AutoBurn function [AB] when you think the PeA is good.
3. Do the burn manually, without AutoBurn function.
Method 1. usually puts me about 0.3Gm at PeA with Mars (which is coincidentally about the same as the nominal mission offset)
Method 3. I can usually get the PeA down to 0.15Gm at Mars.
The largest PeA with Mars at the end of the injection burn that I can still get an accurate landing from is about 2Gm.
Hope this helps
Brian