Put in DOT3 instead of DOT4. Problem?

[Mark's 240]

Hi,

After buying my 240 I checked over the brake system and changed the brake fluid. I've done this several times with other cars. The car is a 1992. Thinking DOT3 fluid has been the standard for years and DOT4 is a relatively new invention, I put Prestone Synthetic DOT3 fluid in my Volvo. Just bought a Bentley manual and it warns against using DOT3 fluid and only use 4 or risk brake system failure. Have I made a big boo boo? Should I change the fluid out and replace it with DOT4? Has anybody had any problems with this?

Thank you,

Mark