It takes awhile to get the hang of the correct amount of spray baste, you want light but thorough and not so much as to soak through the fabric or make things really unpleasantly gummy. If you do overspray, don't despair, just fluff out the project for a couple of days and ignore it, then try it again, whether that is for positioning the fabric or if your needle is getting all gummy all the time.
You can/should smooth out/reposition your fabric after that first time, especially to get out some of the worst wrinkles. As a new quilter, even being super careful, you probably should expect a few wrinkles even on a smaller project or what some of us call "pookies" which can somehow get big enough to stick a toe in, yet the outer edges still look remarkably consistent. A plain white sheet is a pretty unforgiving quilt back, prints can hide a multitude of problems.
I used my 6.5x24" ruler to help sweep out the wrinkles, sort of the same thing as when you are putting on wallpaper.
Typically people start out with too much spray baste and they can stick their fabric together into perma wrinkles pretty easy, only way to get out of that is to very carefully straighten things out and then stick them down correctly before they go back to what they were and now want to be.
Pin basting is using safety pins to temporarily hold everything down. You need a lot of safety pins (couple hundred for a queen sized project) to do it correctly, the idea it that you can't put your hand down without touching a pin. There there types of pins and things to do to help, but it also involves getting down on the floor for some of us (I'll do a lot of things on the protected foam mattress like spray baste, but I don't like to pin on a water bed, even if protected!).