baring some unforseen accident you will do this. You seem to be in good shape, you just need more saddle time. Cascade Bike Club in Seattle has a pretty good training chart, mileage for the STP. (Seattle to Portland by bicycle)

http://www.cascade.org/EandR/stp/stp_mileage.cfm

The STP is like 2 centuries back to back. You won't even be riding that long. The reason I think you need more saddle time is to make sure everything works. (you, gloves, bike, seat, etc.) build up your time between now and July so that you're comfortable riding 50-60 miles a day. (no chafing, saddle sores, etc.) good luck!