Depending on the color of the wood the minwax spar may not have been a good choice. If it is light, the finish will yellow as it gets older but if the bath isn't very sunny may take a long time. Anyway the between the coats sanding should be done with 220 grit sandpaper or an alternative most of the time I use an extra fine Glit sanding pad. It's a 1/2" piece of foam with the sandpaper adhered to one side. It's a bit easier and more comfortable for hand sanding. Once the sanding is done clean the dust off and spray the final coat in the same manor. Try to overlap each coat of spray so you don't have streaks in the final finish. You layer the finish kind of like a roofer puts down rows of shingles, one row overlapping the previous.