On Monday I believe I came in contact with pre come that may have contained sperm. My partner and I were not protected butvhe did not enter me but was attempting to. My period came on today it is very watery and bright I believe it might be implantation blood. I took a pregnancy test but it was negative.

You're having a period. That's probably not implantation bleeding. Implantation bleeding, if it occurs, is usually more spotting then anything. Having your period you shouldn't be too concerned.

Pregnancy tests have a high false Negative rate if used before two weeks after a missed period. The hormone isn't in the right concentration to be detected by the test.

You came in contact with sperm this last Monday, as in 3 days ago?

If that's the case, no, it's not implantation bleeding, since nothing has implanted yet. Of course the pregnancy test would also be negative, since you're not actually pregnant 3 days after sex.

Do you know how reproduction works?