I'll be happy to explain any apparent counterdiction you may present, however I think that should be on a topic by it'self. But as for the one you presented is appallingly easy if one reads what is actually written and not reading into it.waters was upon the earth.

Gen 7:7 And Noah went in, and his sons, and his wife, and his sons' wives with him, into the ark, because of the waters of the flood
Gen 7:10 And it came to pass after seven days, that the waters of the flood were upon the earth.

I use ittillics whenever I expound on the Bible so that the reader knows which is the quote and which is my explaning.
Verse 7 is misunderstood as saying that Noah entered the ark, and it began raining 7 days later. But that is clearly not what it says.
It said he entered because of the flood. But the translaters left out the word 'coming' before the word flood.
Then vers 10 says that the flood was upon the Earth after 7 days, meaning by the 7th of the 40 days and nights of rain the Earth was beginning to flood.

Gen 7:11 In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
Gen 7:12 And the rain was upon the earth forty days and forty nights.
Gen 7:13 In the selfsame day entered Noah, and Shem, and Ham, and Japheth, the sons of Noah, and Noah's wife, and the three wives of his sons with them, into the ark;

Now we have Noah's age to the day when the rains of the flood began. Which was also the day he entered the ark. These verses do not say anything about the flood itself, just the rain that produced it.

The order of the verses is not the chronical order in which the events occured, but rather statements of the events. This is known as Scripture build up. One section may not give all the detail, then another section repeats some of the information given and presents additional details, often misunderstood as being different therefore counterdictory to the former. There is no counterdiction here, but a difficultiy in understanding.

On the day the rains began, Noah entered the ark. After it had been raining for seven days, the Earth began to flood. The rains continued for 33 more days making 40 days and 40 nights of rain which caused the flood.

As for the height of the flood.

Gen 7:19 And the waters prevailed exceedingly upon the earth; and all the high hills, that [were] under the whole heaven, were covered.

Gen 7:20 Fifteen cubits upward did the waters prevail; and the mountains were covered.

This verse doesn't say the water rose ONLY fifteen cubits, but after giving details of the flood lifting the ark in verse 17, then in verse 18 the waters are still rising and prevailing over land. Here in verse 19 the flood prevailed over all the land and all the high hills were covered.
AFTER that the waters continued to rise fifteen more cubits, which was enough to cover the mountains.

Done quoting scripture. Keep in mind that the oceans and icecaps do not contain all the water of Earth. There is water vapor in the atmosphere, and plants and animals, and we humans are all made up of more water then anything else.
Some water has been converted into other materials over the years so the actual amount of real water is and should be much less then at the time of Noah's flood.

Hope this anwsers at least some of your questions. I'm not trying to show off or trump anyone. The Bible should be taken literally. But there are exceptions too, such as figures of speech, and places where the customs of the people of the time
are taken into account.

Taking the Bible literally does not make my head hurt, but when theologions and other self proclaimed experts interpret the Bible to their standards, and use it to propound their beliefs, the confusion it causes for those who don't know the book very well occasionally gives me big headachs when I try to explain the truth, because I often and erringly get associated with those bubblehead, hypocritical idiots, who don't know what they claim.

However it is worth it when I confront some high flueten Reverend or Pastor with more PhDs in theology then I have years alive, and show them how stupid they really are, by making the Bible plain enough for anyone to understand, and show they are clearly wrong.

That kind of trumping I love to do and practially live for.

Hey I gotta get out of here and go to work.