You got pre-approval, not approved a loan, so BOA could not lock the rate for you.
Since RE market changes quickly, usuallly the Pre-approval letter is valid for 30 - 60 days. If you make offers on REOs, then the sellers (banks) might require buyers get another pre-approval from their own banks (such as Countrywide, WellsFargo, Indymac...).
Need to find a property and accepted by seller, then apply for a loan. After approved, then you can lock rate.
Looks like the rate quoted for you was lower than the current rate. So be more active in looking for properties.
Prices are much lower than 2 years ago and interest rates are low. There are many homebuyers and investors looking for properties. Good properties with reasonable asking prices always have multiple offers in California, So keep looking and keep making offers, but be realistic with the offering price.
If you over-bid the price, then your appraiser might not be able to get comps for your winning price. Many properties are back on the market because buyers cannot get financing. So don't over bid unless you have enough down payment to cover the difference.
Please feel free to contact me at (925) 683-1332 if you need more information or need assistance.
Good luck with your home searching.
Real Estate investment Consultant & Realtor