Changing rims

[Painkiller]

Front or rear? Did you get the right length spokes and nipples? Your first time will always be a challenge. You need only start the nipple a couple turns til you get all the spokes in. pay attention to the cross pattern. Then tension evenly all spokes as you go. slightly elliptical is normal when starting to tension and can be corrected as you go. It is best to have a truing stand for this. Then you will need to "Dish" the wheel so it centers in the frame, This can be done by checking on the bike, remove and adjust and check again. I find even pre-built sets can use tweaking here and there. Since you are committed, Keep going. there are plenty of books and videos on the subject to get you thru.