Can I accientally bid against myself?

Yes.   Contrary to popular belief, you can actually bid against yourself if another bidder comes in between you and your second bid. In other words, if you snipe an item with a proxy bid waiting, it is very likely another bidder will intervene and raise your price.

If you insist on bidding both ways for a must-have item, contrary to our advice, then make sure you manually "snipe" close to the end about 10-15 seconds prior to closing, as opposed to several days before. This will minimize any pricing escalation.

Also make sure you understand why timing matters in Why Does BidSlammer Use 5 Seconds?.

In this case you are much better off spending your time protecting against human error than you are worrying about the very-unlikely chance you would miss due to lag.