Hello,
If I do bad on an AP test or on multiple tests (get 3’s), should I report them to colleges? I’m talking about selective colleges such as ivy leagues.
First, a 3 is not bad. But no, you should not report a score <3.
The issue is the 3. Can be problems if you report it and problems if you don’t. Matters more for courses related to your potential major. Once an OP mentions Ivies, you have to factor in the competition from other applicants.
I don’t think the subject matters. I personally see no issues with reporting a 3, even for HYP. As @lookingforward says, there could be an eyebrow raised if you do report a certain score and there could be an eyebrow raised if you don’t report a score.
Getting back to the original poster who asked:
[quote]
If I do bad on an AP test/quote
First of all, as mentioned upthread, a 3 is not a bad score. Second, why are you stressing about hypotheticals? AP exams are 9 months away. Score 5’s and the question becomes moot. 
My son has two 5s, AB Calc, English; two fours, BC Calc and AP Euro; two threes, APUSH AND AP Bio; and a TWO! in AP Chemistry. Most schools don’t give credit for a three in APUSH, and a two in chemistry is pathetic (partly a reflection on the teacher, IMO, but…). I wonder what it looks like if those two scores are conveniently missing, or at least the chemistry score.
As previously mentioned, a 3 is /not/ a bad score. I personally do not think that AP scores play a big role in admissions-- certainly if you had a string of 5s it would add to your application, but I don’t think you would be penalized for reporting lower scores. I would definitely send anything above a 3, and below that, its up to you. Ivy’s and other top schools are looking for students who are more than just a test score, and as long as the rest of your application reflects your passions/interests/intellect, the AP scores are not going to matter. Best of luck!