Can a non-treponemal test for syphillis be a false positive due to ulcerative colitis or uti? it is a faded line 4 weeks after potential exposure?

For the large majority of false positive syphilis blood tests, there is no known cause; and ulcerative colitis is not known to raise the chance of false positives. That said, your question is confusing anyway: tests that produce a "line" generally are treponema-specific tests. But maybe in your country there is a non-treponema test done in this way. Discuss with STI or infectious diseases expert.

There are a number of conditions known to cause false positive to RPR or VDRL (nontreponemal ) test. Positive nontreponemal test has to be confirmed by treponema specific test, which will clear your suspicion and apprehension in case your test result was really a false one.