need some advice..

hi so on may 9th we found a  female stray cat, or rather she found us. We decided to keep her, we took her to the vet, and told us that she didnt feel any kittens and didnt think the cat was pregnant, however because her nipples were a bit more prominent, that there is a chance that shes in a very early state of pregancy that even the vet could not detect yet. (this vet visit was last friday may 24). 

Since then me and my boyfriend have been very worried about the possiblility of her being pregnant. neither one of us have any experience with pregnant cats, ive looked at every website about cats pregnancy i could find, and have confused myself even more as to wether shes pregnant or not. 

so heres my problem, the only low-cost spay neuter clinic in our area, has a 3month wait!!! i have put her on the list, then called back to tell them i was worried she was pregnant and we can not afford to take care of kittens. Someone called me back and said that because a vet didnt think that she was pregnant that for now they would just keep her on the list, but to call if she starts to show signs that she is pregnant, and they would see what they could do. 

We are going to see family from june 14 th to the 21st , my sister will be watching the cat (she has 2 cats but they are both fixed). 

so what should i do? if i tell them i think shes pregnant, and take her there and they say shes not, will they turn us away and we have to go back on a wait list? or should we wait and see. she has a booster shot appointment on june 25th, should we wait until then?

ive put a few pictures of her, i know this alot of questions. im not sure what to do, and any advice would be very much appreciated 
sleeping

I would think that by June 14th, you should definitely know if she's pregnant, since you've had her since May 9th, and I'm presuming she hasn't been with a Tom Cat since that time.  That would make her at least 5 weeks along by then, at which time her abdomen should show noticeable swelling. 

Is she showing ANY other signs?  For example, is she eating for 6 ?  I know you haven't had her that long to know if her eating habits have changed, and if she was a stray, she might be eating more than usual just because she was a stray (catch 22)

I would probably wait at least another week to see if she starts "showing", and if she does, take her in and see if they'll do the spay early...seems like that's your only option. 

opps sorry i meant we found her on the 19th my bad. and i think i will wait and see